If you can't start a conversation, you need to start doing an activity where other people will talk to you. Start doing a sport, volunteer at an animal shelter or take a class on something your interested in. The extroverts will find you if you're around them long enough for them to notice you.
Like prior post of @miratellia
First: try to find something that you really deep down want to master. Like a sport or craftmenship, if you don't know yet pick one and start from there
Second: concentrate on the goal, start working on that, it will probably break down in steps, where along the way you will probably need advice or help,
Third: each step explain what step you want to make and the question you have
By concentrating on something exterior you will make conversation easier
Get a part time job in retail. Limit your availability to your days off. Earn money while you get used to people. I promise to God your give a fuck will shatter in less than 6 months.
Go to a bar or some sort of festival. You don't need to drink, just be there, observe people, let them get within talking distance, then comment on something you see to them. If conversation starts, good. If not, try again another day and chalk it up to you getting comfortable with interacting
Start by making random small talk with retail workers. They get it all day every day, they're paid to be polite, won't take it personally and the best part is if you go to a store you don't normally visit, you never have to see them again.
Do not try to hit on someone who is working retail, however, as this is heavily frowned upon.
But for practice it's ok
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