Translation:I am going to buy a desk the day after tomorrow.
There is no special future tense conjugation in Japanese! You just use the present tense. The use of "tomorrow" is the only thing that indicates the future tense.
If you think about it, the present tense is weird in English and most other languages. It's considered the "default" tense. However, if you are describing a single action, you rarely if ever use the present. The present is an infinitely narrow slice of time; if you did something a mere second ago, you use the past tense ("I did it"), and if you will do something a mere second from now, you use the future tense ("I will do it"). If you are actually doing it while speaking, you don't use the present, you use the present progressive ("I am doing it.") The use of the present tense to describe a single action is rare to nonexistent! The present tense is common when describing things ("The car is red"), though, naturally, and is used to describe behaviors and habits ("I go to the store every week.")
So, consider the sentence 「お店に行く。」 Taken on its own, this could either be the present or future tense, so it translates to either "I go to the store" or "I will go to the store." Like so much in Japanese, the context determines which interpretation makes more sense. In a vacuum, the statement "I go to the store" sticks out as odd, for the reason listed above—you don't use the present tense to describe a single action. However, as an answer to the question, "What do you do when you need to buy milk?", the response "I go to the store" makes a lot more sense, and "I WILL go to the store" becomes a non-sequitur.
What I'm getting at, is, there are actually very few situations where the present and future tense using the same conjugation might be confusing, and those situations can be cleared up by adding context (such as the word "tomorrow".)