The afternoon is dedicated to walking and shopping! Head for the Plaça del Poble. This is a very interesting square, located on the top floor of the government building (free access). From here you can enjoy a splendid view of the valley and the mountains. The square is also a popular local gathering place, especially in the evenings.
It would be a shame to come to Andorra and not do a bit of shopping. All international brands are tax-exempt in Andorra, so no tax! Given that tourism and commerce are the main economic activities in this small country, it's only natural to find a dozen or so shops selling clothes, shoes, make-up, perfumes, jewellery, technology, home decoration, and so on. The best-known shops are concentrated on Avinguda Meritxell, especially the big department stores such as Pyrènèes Andorra!