Because of the right of public access in Sweden, there are a lot of tourism focused on experiencing the Scandinavian nature and our wildlife. The rule of thumb is “do not destroy, do not disturb” which means that you leave a place just the same as it was when you arrived.
If you are hiking you’re allowed to spend a few nights in one place without asking for permission from the landowner, as long as you are not disturbing someone living there. For example; no camping in someone’s backyard, or on a field where a farmer has crops planted, or on newly replanted forest.
The right of public access is however not applicable to fishing and hunting. To fish you need special permission, a fishing card that are sold by landowners or fishing conservation agencies (fiskevårdsförening in Swedish) and special rules for how much and when you are allowed to fish. During spawning season, some fish are protected in certain areas because of their declining numbers, and there may be certain rules for catch and release or if you intend to keep your catch.
If you are interested in fishing in a certain area you can contact either the municipality in question or the tourist agency in that area, they have the information you need to get in touch with someone selling fishing cards.