So my sister's boyfriend tells me about this game all the time so i finally decided to download it, but there are so many champions to choose from I have no idea who to start with. So does anyone recommend a certain champion/champions? 
 
 
 
fun fact: my sisters dog is named Mundo as in the champion Dr. Mundo.

If you look under champions in your summoner profile click on recommend (it's on the left side)
 
Now if i were to recommend a champion, someone like Ashe or Tristana would be good
you'll learn about positioning, last hitting, soloing and such through them.
 
Kennen will teach you about energy management among other things and he's rather forgiving, like Tristana is.
 
I recommend you don't get too attached to characters like Tristana and Kennen before you've tried most champions, because they sorta have an outta jail free card.
 
EDIT: 
For jungling Warwick is probably your best bet as a starter.
Galio will teach you about tanking and supporting your allies.
Annie is a good first time caster champion.
 
You should obviously try out every single champion, but the suggestions that i've given you should get you started.

I started off with rammus, I can't reccomend trist mostly because she seems to be complete garbage. You'll make the most friends, and step on the least toes, if you pick some form of support instead of yet another squishy carry.

Trist is a very strong carry. Yes she is squishy, but she will teach you about positioning.
 
Like i said in my first post, try out every single champion and see what you like. :)
 
@beej: is right though, support is the best way to making friends.

Ashe became my main after trying her out for the tutorials, many many hours laters she's still my main =D 
 
In fact, don't play her, she's mine >_>

Hey Jade, are you on EU or US?

Any of the 450 IP champs are good to try out as each are designed to showcase some particular character type or play style. 
 
Tristana is a very strong attack damage carry, one of the strongest in the game in fact, but playing her can be difficult. I played her for my first couple of weeks with the game and was frustrated at how often I died. You have to be very cautious about positioning with her, because one mistake can get you killed so you have to remember to always be on the outside of a fight, poking with your range, staying out of threat range of the enemy. 
 
I'd agree that most of the "recommended" champs are good to start out as like many of the 450 IP champs, they will showcase a type or style and you can find what you like best. Personally, I'm not too fond of squishy characters as I like to play too aggressive, which just results in me dying if I'm too squishy. 
 
It's a good idea everyweek to jump in a custom game against bots and test out each free champion each week. It will give you a feel for each champion, you'll understand them a lot better when you play against them, and if you have fun with someone, you can try them in a real game.

Try the free ones, see what you like and go from there.

warwick is alot of fun and very good to learn with. i've never really played any ranged characters.

Having not played the game since the closed beta, I'll recommend Ashe as the easiest beginning champion.

" warwick is alot of fun and very good to learn with. i've never really played any ranged characters. "

While Warwick can be effective in the lane, there are better choices. :)

" @crapneck said:

" warwick is alot of fun and very good to learn with. i've never really played any ranged characters. "

Warwick can actually be an effective laner as well. I watched Guardsman Bob on a stream a week or 2 ago go Lanewick in the mid lane vs. Ashe and not only beat her but kill her twice. "

Guardsman Bob does have that crazy habit of going mid with melee champs. I guess it's his thing.

As far as recommendations, Sona is a great support to try out. I loved Tristana on my way to 30, but I don't have the best position so my ranged carry is pretty weak.

" While Warwick can be effective in the lane, there are better choices. :) "

" @JokerSmilez said:

" @crapneck said:

" warwick is alot of fun and very good to learn with. i've never really played any ranged characters. "

Warwick can actually be an effective laner as well. I watched Guardsman Bob on a stream a week or 2 ago go Lanewick in the mid lane vs. Ashe and not only beat her but kill her twice. "

Guardsman Bob does have that crazy habit of going mid with melee champs. I guess it's his thing. "

I played a lot of DoTA back in the day and always knew that I liked close range, fast hitting melee characters. 
 
So I figured that would be the same with LoL and had played that way ever since.  But about a month and a half ago I decided to switch to a mage playstyle instead and turns out I'm a much better player in that style IMO. 
 
I'd say don't look for a specific champion to learn the basics of positioning and shit because you're going to learn all of that from experience anyways.  Learn the bare fundamentals from the tutorials, then play a style that you think you'll enjoy because that's really what it's all about.  You're going to lose a lot, and die a lot. But it's part of the game.  Learn the skills of whoever you choose and think about the ways they can: a) fuck up your enemy.  b) take hella damage from your enemy. or c) help out your teammates. 
 
Then after you learn the game and become a better player in general, don't be afraid to go on a losing streak again learning how to play a totally different style of character. 

Also, for the love of god, don't lock in immediately. Talk with your team about what decent composition will be. 

Play a tank, a melee character, a ranged dps character, and a mage off of the recommended list. Then you will know which kind of character you would like.

Play a tank or support. After you learn the game try out a carry like Ashe. Don't go to the solo lane until you figure the game out.

Ashe is really easy to play as.