Some time ago I saw on google how it is sort of possible to make an USB stick from an internal SSD (a special casing with USB cable is needed). Is it the only way, or are there specific devices designed to accommodate internal SSD for external connection to a laptop via USB port?
M.2 is the name of the connector on the end of the drive. There are different types of M.2 connector. Most modern SSD M.2 drives are M Keyed. You need to make sure that the enclosure you use is compatible. Most modern enclosures will be.