In order to drill slots you need chisels according to the lvl of the equipment you wish to slot.
Steel chisels are for example for lvl 30 and below gear
You simply purchase such chisels, right click the chisel and click on the equipment you wish to slot.
One-handed weapons and relics cannot exceed 3 slots.
Two-handed weapons can have up to 6 slots.
The question to your attack was actually already answered in your other thread.
You might want to re-read, what Izzeth said should answer you how to improve