Adding spiders and insects to your terrarium?

Hello.

I've been browsing this subreddit the past week or so, and I'm pretty inspired to make my own terrarium. I've seen that some people how living creatures in their own, from insects and fish to amphibians.

It seems as if spiders like to "magically" appear in people's terrariums, so maybe they like particularly like that environment. If I put small spiders in mine, I'll of course need insects to feed them. Which insects? Which species of spiders? Should I buy the spiders, or just go find them nearby (small funnel spiders are very common around here).

Any help would be greatly appreciated.