Lots of choices. Simplest is to put them into individual sleeves, which also takes up the least space. Disadvantage is that they aren't really displayed then.
You can buy purpose-made albums for covers, which are produced by Lighthouse and other manufacturers. https://www.ebay.co.uk/itm/Lighthou...FDk9sYgrn6Iw
You can also buy sleeves (usually with space for four covers on a two-sided A4 page, which will fit in a ring-binder. Here's a UK versionhttps://www.ebay.co.uk/itm/250-Firs...em27b7d2f1da
I mounted my French FDCs on quadrille pages in albums, using photo corner mounts. If the paper's thick enough and you use interleaving, you can get four on a sheet by using both sides. However, I did start with a lot of old leaves that I could re-use and a lot of old binders to out them in.