If you followed our route, upon arriving here from Rolling Fields, you should reach a glowing den by the side of the central lake. From here, all you need to do is go forward (north) towards the big staircase leading up to Motostoke. There will be two stretches of tall grass, one nearby on the right and another further ahead, by the lakeside.
When you approach the second stretch of tall grass, by the lake, be wary of a strong Pokémon (Xatu) flying around towards the right (east). If you're brave, there's a sparkling spot smack back in the middle of the dirt area, where the strong Pokémon is keeping guard. Your reward is a hidden Poké Ball.
Keep going until you've gone past all of the tall grass. There will be another glowing den that's somewhat near the lakeside. Ahead will be a big patch of dirt, with dirt paths going left (west) and right (east). Nearby to the right, there may be another fisherman who will offer her random item for your Watts. Crucially, Motostoke will be a few paces forward.
Without further delay, run towards the big staircase. However, before going up the stairs, head over to the left. There, you'll find the Camping King, who will help you change the colour of your camping tent and evaluate your Curry Dex. Also, there's a Watt Trader who's running a shop, where you can spend your Watts.
Watt Trader's Wares
There are several Watt Traders located in the Wild Area. Each one sells a special type of Poké Ball, a Wishing Piece (used to trigger a Max Raid Battle) and a random selection of Technical Records (TRs). Like TMs, TRs can be used to teach moves to certain Pokémon, but they are single-use items (like TMs in the past).
By the way, the amount of Watts needed to purchase TRs is pretty high, especially in comparison to the Watts you can earn by interacting with dens. So don't worry if you can't afford many (or any). After completing the game, you'll earn more Watts than usual, so that's the best time to stock up on TRs.
Those fellas will be standing there all day, every day, so it's good to be acquainted with them. Once you're all done and dusted, make your way up the stairs.
The Pokémon found here aren't much different to those in Rolling Field. Most of the good stuff is in the lake itself, which you can't access right now.
That said, you can fish from the lakeside near the entrance to Motostoke. Besides Magikarp, there's Goldeen, Shellder and--if you're lucky--Wishiwashi. There's a Fire Gym coming up soon, so consider training one of those if you don't have a good Water or Rock-type.