How can I learn to be more sociable with people?

All my life I've been raised to stay indoors and not answer phone calls or give my number away ever since I was little. We had over the top worried parents and we still do but they've loosen up a bit now and allow us to go out. I'm 22 but the majority of my life I've spent alone not doing much. So even at this age in time I feel like I get stumped on MANY things when people talk to me. I'm so gullible as well. I would love to learn how to talk to people and hold convos with them instead of small talk. But I just don't know how. When I want to. I lose interest because I'm used to being quiet. But I really do want to learn how to talk about a little bit of everything so that I don't look so stupid. I feel illiterate as well. How can I improve my social skills? I don't always want to say "I don't know" or seem to be thinking too hard on what to come up with to say. What can I do to teach me how to talk easily with people? And I still don't go out often 'cause I'm used to not going out.