If you Google "Kirchoff's Voltage Law" and read the first few definitions that come up, you may still feel like you don't know what it is. Here is what it is in practical terms:

And here is a quick aside on measurement and schematics which is particularly relevant to KVL:

And here's an example of how I draw it in CircuitLab. Yes they include that little symbol that looks like an old-school VU meter, but you don't need to if you draw it by hand.