The 5 x 5 is one of the tired and true ST protocols out there for those that want to built strength and some mass.
It is focuses on the big compound lifts ( Squat, Bench Press, Deadlift, etc).
There are two versions of it:
After a warm up of a couple of sets, you do 5 sets of 5 reps with the same weight, when you can do all 5 reps in all 5 sets, you increase the weight ( how much depends on what exercise you are doing but usually 5-10 %).
The other method is you warm up with an increasing amount of weight over the first 2 sets ( doing 5 reps per set) then you do 3 sets of 5 reps with your working weight, increasing weight when you can do 5 reps for all 3 sets.
EX:
Method 1) squat - warm up with 100lbs for 5 reps, 150 lbs for 5 reps, 200 for 5 x 5
Method 2) squat - 5 reps with 100lbs, 5-reps with 150lbs, 3 est of 5 with 200.
The differences?
Method A allows you to push more total weight BUT progress will be slower.
Method B allows for quicker progress BUT you are moving less total weight.
It depends on what your end goals are.
Typically you would use the 5 x 5 method on either every exercise you are doing IF you are doing only a few exercise OR you do it only on the compound lifts and not on the other ones.
EX:
5x5 on squat
3 x 8 on Chins
5 x 5 on bench press
or something like that, again depending on your goals.
Psalms 144:1
Praise be my Lord my Rock,
He trains my hands for war, my fingers for battle !