Je suis en première année.
This literally translates to "I am in the first year."
Here's why this is used:
* "Première année" is the most common term for the first year of high school or college in French.
* "Freshman" doesn't have a direct translation in French, so this is the most accurate way to express the same idea.
You can also say:
* Je suis un élève de première année. (I am a student of the first year)
* Je suis en classe de première. (I am in the first grade) - This is more common for younger students.
The best choice will depend on the context and the specific level of education you're talking about.