"How do you say 'and' in American Sign Language?" Be aware that there is much grammar involved that this sign is almost not used.
ASL signs for 'and'
Used to connect words of the same part of speech, clauses, or sentences that are to be taken jointly.
Pronunciation (sign description): Dominant, loose "5" hand in space in front of signer with palm orientation facing in (toward signer) moves sideways to the right if right-handed at the same time the hand transforms into flat "O" handshape
Although this conjunction "and" is an English usage, this ASL sign is not directly used in ASL and isn't often used. Rather, it's conveyed in a different grammatical structure, using contrastive structure, ranking/listing grammar, ALSO-conjunction, and some more other ways.
Another way of using "AND" in ASL is the conjunction "ALSO". Beginners typically use "and". Not frequently though, another use is PLUS in specific contexts.
The best way to learn "and" and "also" in ASL is to immerse in Deaf community for long enough to understand the use in contexts.
Hearing Culture: Y and Z
One of some observations is that English-speaking hearing people usually use "and" between the alphabetical letters "Y" and "Z" when spelling out the alphabetical order. E.g. ... U, V, X, Y, and Z.
In ASL, Deaf people including deaf children typically fingerspell out the alphabetical order all the way down to Z without the little word.
My bilingual toddler, whose first language has been ASL from birth, practiced the alphabetical order with me from A to Z. But, later her hearing teachers taught it differently at preschool. The preschooler fingerspelled with the English word "and" in it (that's how I became aware of it for the first time).
Fast forward, as of this writing, I'm curious whether she still uses it or rather had assimilated into ASL/Deaf culture. I asked my 11-year-old kid to fingerspell out the alphabetical order. She fingerspelled all the way down to Z. Right on!