A quarter note is one beat. Cut it in half and you have two eighth notes, counted "1 &" — the number on the beat, the ampersand on the upbeat. Eighth notes are the first thing you really subdivide, and they unlock most of the grooves you'll meet in the first year.
Each exercise below stays on the snare so you can focus entirely on the counting. Say the count out loud — literally out loud. Internal counting comes later; right now your mouth is part of your timing.
How to Practice the Count
Set the metronome to quarter notes and make your voice louder than the drum. The click marks the numbers; your "&" has to land exactly halfway between clicks with no help. When a rest lands on the beat (Ex 4), keep counting through it at full volume. Silence in the hands never means silence in the count.
Two failure signs to listen for: the "&" drifting late toward the next number, and the count going quiet exactly when the rhythm gets hard. Both mean the same thing, so slow the tempo until voice and hands agree, then bring it back up one notch at a time.