Catsuit, unitard, bodysuit, surfsuit, skinsuit - all terms that relate to a form-fitting one-piece garment that reaches from shoulder to leg, usually extending to ankles and wrists. For the full experience, Zentai suits have gloves, socks, and a hood too, to cover everything! There are practical and aesthetic reasons for wearing bodysuits - from the protection against UV light afforded by surfsuits to the ease of movement and beauty of a dancer in a unitard - but for myself, I find hoodless gloveless catsuits entertaining and occasionally pleasant for lounging and pyjamas.
Here are a set of instructions with photos covering construction of a catsuit from measurements to sewing.
Follow links marked with to step through the simplest and most popular suit: a catsuit with a zipped seam at the front or back. I'll be adding other options as I convert from the old pages, but all options presented from this page will be described in comparison to the basic suit.
Just remember: everyone makes mistakes - that's how we learn.