Do not can in anything bigger than pint jars.Sterilize jars,rings,& flats in boiling water. Fill hot jars with very hot (near boiling) salsa. Wipe off outside of jars, espcially the where the lids go. Place hot flats on top and screw on rings. Place in canner that has boiling water and process for 20 min. Remove and let cool in room temp. You should hear popping as the jars seal.
Some people skip the boiling water bath part as jars will seal before then, but to be extra safe I always orocess for 20 min.