If you have a spreadsheet, where the first and last name are in two different cells, but need them into one for e.g. if importing your data into a website, some may only recognise a "Full name"

Make a column next to your First name and Last name, e.g. Full name

Type in the name into your first cell for Full name, then underneath this cell, start typing in the name for the second person, you will see Excel will recognise what you might be trying to achieve, when you see the other names appear, simply press Enter, and it will populate all the other names for you