This comp is very simple in that it aims to put 6 Skirmishers together to buff up Jax. The buff is also nice as it helps all of your Skirmishers deal some extra damage the longer the fight goes on
Go for this comp if you can make good Jax items and have a good start with Skirmishers.
Level up to 4 early if you want to start a win streak. Level up to 5 to try and continue the streak.
If you're weak in the early game, you can opt to save gold and lose streak instead.
At Round 2, level up to 6 regardless of your start. Put together the strongest team you can.
At Round 1, level up to 7. Roll down to stabilize your comp if you are weak. Afterward, save up to hit level 8 and complete your comp.
You mainly just want to have as many Skirmishers as possible while using other units you find to fill the other spots.
Hitting 6 Skirmishers gives the team a big power spike, but if you can't find them all, use supporting synergies like Nightbringer or Dawnbringer.
Quicksilver is a very important item on Jax because he is a melee carry. You don't want to build it early since it won't be very strong, but make sure to keep it in mind when building items in the mid game.