"Dělám čaj."

Translation: I am making tea.

[koriikki]

can i also say varim caj? is this one more natural?

[VladaFu]

Yes, it is accepted.

[holzfaeller.marc]

Why isn't "I make a tea" accepted?

[VladaFu]

Tea is uncountable, if you want something countable, you can have a cup of tea. (Yes, I know one can sell teas and coffees, but that is a different thing.)