I'm planning on painting the breeze block wall in my garage. Do I need to use a specific paint type or am I ok to just use left over matte?
Also, is it safe to paint the floor?
You can use a left over matte finish (I'm guessing this is what you were talking about), but the blocks will soak it up and you may need a few coats for a decent look. I would start with a masonry primer first that will seal and fill the pinholes, then you can topcoat it with whatever you want.
You can paint the floor, but you're going to have give more information: Is it new concrete? Is it stained or sealed? Is it painted right now? Do you plan on parking cars on it?
H&C Shield-Crete and the Acrylic glaze to go over it may be your best bet.
You could also used watered-down PVA glue to seal up the pores in the concrete and prime the surface for paint, as this is a cheap and effective way of doing this, and will reduce the amount of paint you need for good coverage.
Note that regular PVA cannot be used to prime surfaces prone to dampness or getting wet.
Three years ago, we painted our breeze block wall red with Behr exterior paint that was mold/mildew resistant. It is still holding up and looks like it was painted yesterday. Unfortunately, it took 3 coats to get total coverage. I did pressure wash the breeze block before I we painted. Besides that, we didn't do anything else special.