Hi Rowan White
Not a stupid question at all. In the past the only way to handle this was to use MultiTerm Convert and the process you would go thorugh would be to convert the Excel to an XDT (termbase definition file) and an XML (contains the terminology); then create the termbase in Multiterm with the XDT and then import the XML. So quite an onerus process.
Today you have two simpler options.
1. Use the Glossary Converter which is a drag and drop process to get your termbase
2. Use the Excel spreadsheet itself (saved as XLSX) as the termbase directly
These two articles might shed some light on all of these options:
Using the Glossary Converter
Using the XLSX directly
Using MultiTerm Convert