I would put it in a zippered pillowcase, as a mesh bag might let fuzz out into your washer.
Also, put a couple/few pairs of jeans in with it to add agitation.
When they say SMALL amt of laundry soap, they mean SMALL! Like, a tablespoon! I put 1/4 cup or so in the first time I felted & there were SUDS everywhere!
Otherwise, just GO FOR IT!! We've all had the first time jitters....and it all turns out GREAT in the end! Very UNlike my first "date".