The trading post is a little log cabin located in the mountains. There are two signs that say "Wandering Oaken's Trading Post" and "And Sauna."
As Anna journeys out in the mountains searching for Elsa, she finds the trading post and goes inside to buy some comfortable winter clothing. Inside, Kristoff enters and the two eventually meet. The seemingly happy and calm Oaken is angered at Kristoff after he calls him a "crook," and kicks Kristoff out of the store before returning to his usual self. Anna then gets the idea to have him guide her to the North Mountain in finding Elsa.
Olaf's Frozen Adventure
To be added
There is a plush Mickey Mouse on one of the shelves in Wandering Oaken's Trading Post and Sauna.
It's unknown as to how Anna paid for the items she bought, since it's unlikely that she had carried money with her. However, it's possible that she sold off her green dress to pay for the items she bought, which is supported by the fact that her ballroom dress hasn't been seen since. She may also have sold her greenish-gold pendant that has the Arendelle's symbol, which is expensive because it's a jewelry worn by a princess. Another possibility is that she promised that she would pay for everything, supported by the fact that she likely didn't bring any money to pay for even the winter gear. Or, she could have told him she was the Arendelle princess and convinced Oaken that Elsa would reimburse him later, and barring that, it's entirely possible Anna did suggest Oaken send a messenger down to Arendelle to collect money.
There are carved trolls on the front porch, like the ones in the film.
The shop has a smaller counterpart named "Oaken's Cloakens" in the Arendelle village. The smaller shop appeared in Frozen Fever.
"Wandering Oaken's" is an anagram for "naked Norwegians". This is referenced perfectly by the fact that the shop also includes a sauna, in which people sit and wear nothing but a towel around their body; thus it makes them the "naked Norwegians".