How do I make my own subreddit, and are there requirements before Reddit lets me create one?

On desktop it's easiest: the '+ Create' menu > 'Create a community' (or go to reddit.com/subreddits/create). Pick a name (permanent, can't be changed later), a description, and the type, Public, Restricted or Private, plus content settings. Requirement: Reddit generally wants an established account, roughly 30 days old with some karma; brand-new accounts often can't create one, and there's a limit on how many you can make in a short window. Once created you're the mod: set rules, a banner and a pinned welcome post. The hard part is getting the first members, so cross-post to related subs within their rules.

The name is permanent, you cannot rename a subreddit after creating it, so get it right the first time. And a very new or low-karma account may be blocked from creating one until it ages a bit.