Because of Andorra’s rugged terrain, there is only one route that connects it to France, and only one that connects it to Spain. Almost all immigration into the nation occurs at one of these two locations.
Visitors from outside the EU should be aware that Andorra is not a Schengen member, and that entering Andorra from France or Spain would (theoretically) end a single-entry visa. However, in reality, immigration does not enforce this. Non-EU people holding a residence permit in an EU member nation do not need a second visa to enter.