At the end of every tattoo session we will go thoroughly through the after care that is needed for your tattoo.
However, the basics you need to know are:
No sub-merging your fresh tattoo in water (swimming, bath, sauna, steam room, washing dishes etc.) for the first week - your tattoo is at its most vulnerable when its fresh, any potential bacteria in the water may get in your tattoo. Think of it as an open cut, you don't want yucky water near it.
Cleaning your tattoo in the shower with warm soapy water is fine, constant stream of fresh water that hasn't sat should be safe.
No direct sunlight, aka don't get it sunburned, if you must go to the beach within the first week or so of it healing just drape a towel over it.
Use an aftercare cream when dry, just a thin layer 2-3 times a day. Some options are Manuka balm, Bepanthen cream, Kawakawa balm, coconut oil.
Wash with warm soapy water
Gently pat dry.
No picking/scratching/itching while it heals
Ultimately if you just keep it clean and use your common sense it will heal fine.