I thank you for your support... I carefully followed the guide, my dex is connected with trustwallet, but I have no funds on the dex! Is it enough to transfer a few coins?

Choosing the right mapper is always a tricky question which heavily relies on what you need to do :) Here would be all available mappers, including the user mapper https://github.com/ElrondNetwork/elrond-wasm-rs/tree/master/elrond-wasm/src/storage/mappers

Each team has it's own set rules, kindly follow up the rules of the project you have interest for and if you have doubts after reading their rules, I could kindly suggest you to ask them as well, usually in their TG group