You should contact the foreign office of the country you come from as they should be able to help you. You could also visit duana.ad which is in Catalan but it has details of immigration laws. Finally, everyone who gets a work permit needs to have an official police report from their home country which has been stamped to say it is official.

When you get to Andorra and get a job, your new employer should help you go through the immigration process.

Hope this helps.

Steve