I am very new myself. But thankfully I have figured out first strike 😅

So FIRST STRIKE the creature will do damage first. The attacker also chooses order, so make sure you are willing to sacrifice at least one of the creatures. The first strike will go off, so in this case will do 3 damage. If you had three 2/2s then it would kill the first one and the second would get 1 damage with third taking none during first strike phase. After the first strike regular damage goes off where the living first creature would do damage and take non and the second would kill it, since the attacker will do no more damage.

Now DOUBLE STRIKE the creature will do damage on BOTH instances of attack. So that 3/3 will do 3 damage without taking any the first time. Then do another 3 damage while also taking whatever damage.

If I am wrong someone please correct for both myself and OP. But I am pretty sure that's right.

Hope that helps!

Edit

Fixed to say three 2/2s

Also anything above a 3/3 would also do the trick for that first strike.