Can I tell someone I'm not ready for a relationship and then getting into a relationship
What is it that's stopping you from getting into a relationship?
I don't want a relationship, I just want sex
That's okay, you know what you want so you should be able to communicate that to people who feel the same way. There are many who are in the same boat with hook ups.
I guess,  I just want sex and I don't want a real date.
I am saying that is fine, just be open about your expectations. If they are DTF then fine. Most people want to know upfront what your intentions are so you don't waste each others times.