Learn Swedish: Du behöver inte använda uniformen idag. - You do not need to use the uniform today.

In Swedish, behöver acts like a modal verb here, meaning it takes the bare infinitive använda directly. Just like we say "you must use" without a "to" in English, Swedish drops the att after behöver.

What would happen if I used får inte instead of behöver inte here?

It would completely change the meaning! Behöver inte expresses a lack of necessity ("you don't have to"). If you said Du får inte använda uniformen idag, you would be expressing a strict prohibition: "You must not use the uniform today."

In English, we usually say "wear a uniform". Is it normal to use använda (use) for clothes in Swedish?

Yes, it is perfectly natural in Swedish to say you använder (use) functional clothing, gear, or a uniform. You could also use the phrase for wearing clothes by saying ha på dig, making the sentence Du behöver inte ha på dig uniformen idag.

Why does the word uniform have an -en at the end?

The -en suffix makes the noun definite, changing "a uniform" to "the uniform". We use the definite form here because the sentence refers to a specific uniform that the speaker and listener both already know about.