What kind of blocks do you have?
wood like 2x4's you would buy at a lumber place. I'm cutting up about 300 small blocks 2"x2" on angles and need to paint all of them individually black,white and different shades of grey. painting with a bush ,not me-spray paint ok but will it absorb and i'll have to do it again? remember i have alot of blocks.any idea what kind of paint i should use?
If you are talking about toy wood blocks, you will need a non-toxic stain or paint because kids will chew on them. If you are asking about concrete blocks in a wall, then you should prime/seal them and then roll on a good quality paint (brushing grout lines).
I believe Ken has provided the answer, it would be good to have more information ie type of blocks, just saying.
If it's cinderblocks that's tricky as they absorb everything. They would need sealed before painting.
If it's wood blocks that's different and you can just paint them.