Could is the past of Can.
It’s used as the past of can to talk about what something or someone was able to do.
Used to talk about possibilities
It could be true that he is the owner of the car.
They could come any time from now hurry up.
Used to ask for polite permission.
Could I see the boss please?
Could you lend me £15
Used to while talking about suggestion
You could try dying it blue.
Could have in if clauses