kowtow i recommend doing the tutorial mode multiple times and also testing shit out in practice mode, which is very good. also, if both people are trying to transition at the same time, the winner isn't determined by stats, it's determined by frame advantage. for instance, if you successfully block a transition attempt, you get frame advantage. if neither of you is at frame advantage and you both try to transition at the same time, whoever technically completes the transition input first will win, because you're obviously not inputting it at the exact same time. however, major transitions can be stopped with transition blocking, and both minor and major transitions can be stopped with transition reversals, which is basically flicking the right stick to the right or left as soon as your opponent starts to transition.
in terms of your half guard question, master thespian's advice is pretty much the worst thing you can do vs a good player. no one tries to inflict damage from half guard because it's just not smart. in half guard, your opponent can do a minor transition to get to side control, and you can't stop him by transition blocking because it's a minor transition as opposed to a major transition. if you think the guy is going to strike, you do a major transition (because that's the only type of transition available from bottom half guard that actually takes you out of half guard). if the guy goes for a submission, you escape it by mashing the buttons. you should never be subbed unless you're gassed (you're gassed when your stamina meter is yellow). if the guy is just holding transition block, you can use a minor transition to bring him from up half guard to down half guard, which doesn't do much but at least he can't strike you with power. alternatively, you can strike up at him from bottom half guard whether it's up half guard or down half guard. either way it doesn't do much, but no one's going to sit there forever and keep transition blocking while they're getting punched in the face. you just have to anticipate what he's going to do and when he's going to do it. the guy on top does have the advantage, but that's the way it should be.
regarding your clinch question, wrestlers can do strong takedowns from the double underhooks position and judokas can do strong takedowns from the over/under position. bjj guys don't have strong takedowns. what this means is if someone is trying to take you down with a weak takedown (anything other than what i just described, for instance a wrestler trying to take you down from over/under or a judoka trying to take you down from double underhooks) you can just hold back on the right stick and you'll come out on top. holding back on the right stick also prevents bjj guys from pulling guard. if someone is in a position to take you down with a strong takedown, you should try to work to a better position in the clinch, which is done by tapping forward on the right stick. the only other way to prevent a strong takedown is to guess which direction they'll use to take you down and to input the opposite direction on the right stick with the same timing as a transition reversal. however, this is a terrible strategy because unless your opponent is very predictable, you only have a 1 in 4 chance of succeeding, and that's if you manage to time it right.
if you have any more questions, hit me up on aim.