How does immersion work? I'm halfway through level 13 but i suppose it doesn't matter much; I have only come as far as Adverbs1. Could I try it now or should I wait a bit longer? And what if I made a lot of stupid mistakes while translating?
You are translating into the language that you are fluent in. Start by reading other sentences. Does the English version make sense? If it doesn't then spend some time studying the foreign language and see if you can improve it.
Scan the article for simpler sentences and titles that you may be able to do.
For clarity, I just wanted to add that DL will determine a user's native language through their settings: I have told my settings "I know English I want to learn Spanish". Immersion expects me to translate articles into English.
However, if I begin working on the mirror course for extra practice (Spanish to English), under those settings Immersion expects me to translate articles into Spanish.