There are several ways to install electricity. What we've seen more often are the plugs installed in the floor, near the wall, that way the electrical receptacle box is hidden under the floor. You would cut a rectangular fitted hole in the wood, insert the box underneath and install the plugs.
Another way is to install a waterproof receptacle box (such as this one) on the outside wall and have the outlet anywhere on the wall. See the two photos below. There are multiple outlets, and even the outside sconces, that all go up with the junction box onto the roof. If your lighting fixtures would be on the walls instead of the ceiling, you can have the junction box on the wall and have all the wires meet there.
NOTE!
It is important that you use flexible/ accordion-type conduits at the "elbows" where they bend, to allow the shed to expand and contract, which only happens vertically. Installing a rigid conduit that goes from the ground to near the top of the shed walls fixes the top wall boards at a certain height, not allowing them to sink with the rest of the structure when the wood shrinks, or rise, when the wood expands, potentially causing gaps between the boards.
Ideally, we recommend hiring an electrician for any electrical work, since the shed is made of solid wood, faulty wiring may cause fire.