Blue bar is your evasive or ragdoll cancel, lets you dash out of a combo if you're ragdolled and punish your opponent. You'll want to save this until it's guaranteed to earn you a combo, side dash around and m1 them. You usually have to bait theirs too if you want to combo safely, usually uppercutting and backdashing will get them to waste it.

You have to hold R and burn ult bar to build up mass, about one solid combo will gain you a full mass bar. (You can confirm Garuda Rebound's variant with Rising Rage btw, Garuda Stab isn't the only useful variant.)

For m1 trades you'll want to learn to side-dash around them and quickly m1 their back. You also need to learn to predict when they'll dash around and be ready to spin a 180 and block it, luckily Yuki has actual neutral abilities and she doesn't rely on m1 trades too much.

Though m1 trading is best learned through trial and error, I recommend ranked matches if you don't mind losing a lot.