You as Master Yi
You're Master Yi and you should go bot or top,I usually go Top. Use your "q" Alpha Strike to harass and your "w" for a sustain if your enemies are harassing you too much. Your "e" can passively boost your attack damage,but when active it can boost the damage on alpha strike. Lets get to the build!
Master Yi's Abilities
Use your "q" Alpha strike to Farm/Harass
Use your "w" Meditate for a sustain to heal if the enemy is harassing you too much.
Use your "e" Wuju Style to Increase your Alpha Strike Damage when harassing.
Use your "r" Highlander for killing a champion and getting cool down refresh on all abilities,or for an escape tool.
As Master Yi you should stay behind your team,let your team poke and once someone initiates your combo will be "e" "q" "r" to win the teamfight. Don't let yourself get caught or else you will die before it even has started.
The Build you'll Use
Start top or bot and get boots and pots. Next,build up to frozen mallet for health then Bloodthirster for Lifesteal/Ad. Get Phantom dancer next then Infinity edge for lots of crits and movement speed.
Lastly,get infinity edge for "Tons of damage"