ごほーし meaning? 18+? I know that's lewd vocabulary but I dont what does it mean?
The word itself is nothing lewd. It's an intentional nonstandard spelling of ご奉仕【ほうし】 "serve / service to somebody". ご is the polite/humble prefix that usually doesn't translate into anything in English.
For the connotation of using the long vowel mark instead of う, see: