Beat and tempo
What's a "beat?"
People commonly use the word "beat" to mean "a pattern (or rhythm) played by drums." The thing you're making when you create and play patterns in these lessons is "a beat."
But, confusingly, there's another use of the word "beat," which means "a regular, repeating pulse that underlies a musical pattern." People tap their foot along with "the beat" in this context.
Tempo
The speed at which your patterns play back is called the tempo. Tempo is measured in beats per minute or BPM. So if we talk about a piece of music being "at 120 BPM," we mean that there are 120 beats (pulses) every minute.
Some types of musical patterns have a very clear underlying beat, while others have a more subtle or implied one. To hear a steady beat, add notes on the Kick line at the positions labeled 1, 5, 9, and 13.
This pattern is so common that it even has its own name: "four on the floor."
Now try adding some notes for the top three rows, but leave the Kick row alone. Notice that no matter what you do in the other rows, the steady pattern in the Kick line makes it really hard to lose the sense of clear pulse.