If you're coming to Thailand for the first time, we recommend to pre-book a room, since immigration will ask for the address where you will be staying.
Generally if we are not sure where we want to stay, we will pre-book a room for a few days, then use those few days to explore the city and determine where you want to stay.
So just give the immigration the name and address of your hotel.
To travel around we are going to be biased and say you should book some time with Chalida, our main Youtube Host. She does tours and will be the perfect guide for you to learn about the city and the islands.