Mac mini 2011-mid and SSD sata 3 can someone tell me, will this ssd disc work on my mac mini, since is sata 3? As I know my mac uses sata 2?

But I'm really novice and I have no idea.
Not sure why you think it's SATA2. According to everything I read, the mid-2011 Mini is SATA3

http://www.everymac.com/systems/apple/mac_mini/specs/mac-mini-core-i5-2.5-mid-2011-specs.html

There are considerations related to garbage collection related to the SSD controller. The safest choice is a OWC Mercury from macsales.com since they are intended for Macs. Others may require installing a 3rd-party TRIM enabling utility.