do i need to secure my cpu with something else, if im using thermal paste ?
No, you should leave it loose so when it gets hot it can fall out of your motherboard and do a little dance around the room to cool itself off!
OK, All joking aside yes your CPU most definitely has to be secured. Thermal paste is just that, a paste (like toothpaste), not a glue and while you could buy a thermal glue you wouldn't want to use that on your CPU.
All motherboards have some sort of mechanism to lock the CPU in place and any type of thermal compound should never be used in-between the CPU and the motherboard.
The heat-sink that goes on top of the CPU (motherboard, CPU, heat-sink, in that order) also has a way to secure itself in place.
The thermal paste goes in between the CPU and the heat-sink. It's important to use enough but, not to much or it could squeeze out and get on to some of your electronics. That would be bad!
I'm guessing you haven't done this before so I would check out YouTube there are a number of good videos about applying thermal paste to CPU's.