How do I combine string variables?

[AiriableConditions]

I'm planning to make something where the player inputs letters in an order to form a level's name, which will then be loaded with each letter as a variable, but I can't figure out how to combine string variables (a variable for each letter.)

Example: "level" combined with ".lvlx" to make "level.lvlx"

I've tried doing table variables, such as {"level",".lvlx}, and I've also tried to use + to combine the string variables, such as Level.load("level"+".lvlx"), since that works in other programs, but it always gave me an error trying to load it.

[Emral]

The lua concatenation operator is ..
"level" .. ".lvlx"