Baitcasting Reel How To

[Sluggoslinger]

This is my first year using a baitcaster. I got an abu garcia 6500 and a 7'6" St. Croix rod. I loaded the reel with powerpro but only enough to spool my Penn 5500SS. My question is, is powerpro OK for a baitcaster reel? Also, how do I cast with it without making a mess out of the line. It seems like if there is any pressure on it, then the button doesn't work. Should I keep my thumb on the spool?

I know this is a dumb question but I had to ask or I am afraid I am going to have a rats nest of line the first time I use this reel...

Thanks!