Maybe I missed it, but they didn't do a lot of explaining about what the safelane is, what it means, why pro dota players run trilanes and offlanes, etc. which is a concept that even after hundreds of games I still don't quite grasp.
Trilanes are run to secure early farm for the hard carry. Off-lane heroes usually have the ability to either take a beating, heal themselves, some kind of mobility or escape ability - best if they can disjoint incoming single-target disables. Trilanes usually operate by having 2 in the lane while a third stacks and pulls the neutral creep camp. You have to stack the creep camp nearest your lane so that the 'neutrals' kill off your creep wave. If you don't stack first before pulling, you will end up with 2 waves of your creeps pushing up the lane. You can use this to your advantage if you intend to push the enemy tower, but generally you want to stack first and then pull. Stacking and pulling does 3 things in the trilane:
1) The most important thing is that it controls the flow of the lane. When the creeps are pulled, the incoming enemy creeps have no opposition and will push up the lane. So if your lane is pushed up to the enemy tower constantly, it makes it difficult to secure farm early game and also difficult to escape if they make a move; you're also more susceptible to getting ganked. But if you pull the creeps, you can then shift the action of the lane to a more favorable position, closer to your tower in case you need to escape, and also easier to farm because the enemy will not be able to come as close to you without risk.
2) It provides gold and experience for the player that is doing the pulling and keeps them out of the lane to allow the other two players to have better experience gain. That is to say that if all 3 were in the lane, the experience would need to be split 3-ways and this would put the players behind in terms of levels as the game progresses, whereas with a designated "puller" you can all get pretty standard experience gains all around.
3) It denies an entire creep wave from the enemy and they therefore miss out on crucial gold and experience.