Primary point about how to catch fish: Fishing is a verb, it requires action and attention. Leaving your line in the water won't get you fish. Your bait is on a hook, you have to actively "hook" a fish.
Wait until you feel a nibble, do nothing, nibble just means the fish caught an edge of the bait. Feel through the pole that the fish is taking several nibbles, this indicates the fish is trying to gobble the whole thing. Once you feel a series of nibbles you have to "set the hook." You set the hook by feeling for that nibble giving a bit of slack and then making an aggressive pull to make sure the hook sets itself in the fish's mouth. Once the hook is set you apply steady upward pressure as you reel, after the hook is set giving too much slack may cause the hook to re-align or lose grip.
There are different ways to catch different fish, the above doesn't work so well with a sword fish or a shark, but for your needs, my advice should be good.
Look up the kind of fish you are fishing for and find advice specific to that fish.
The core principle: Fishing is a verb, it's not a passive act.