There is an eighth note followed by a quarter note, and above them is a little overarching bracket with a little 3 in it. I know this has something to do with the timing, but I have no idea what.
This is for piano, by the way.
Here is a quick example of triplets similar to your description of what you saw:
There are four beats in each measure, but in the first measure, the second beat is divided into three equal sub-beats notated as eighth-note triplets. Three eighth-note triplets fit into the space normally allotted to two eighth notes.
In the second measure, the second beat is also divided into three sub-beats, but in this case, the second and third eighth-note triplets are tied together making an eighth note and a quarter note within a triplet. It's a little unusual to see it that way.
In the third measure, you see exactly the same rhythm, but within the triplet, you see three eighth notes and the second and third are tied. It is played the same way.
It's a triplet. This means that the rythmic pattern of the notes within the bracket is at odds with the overal meter of the piece. Relative to each other, nothing changes, i.e. the quarter note is double as long as the eight note. But relative to other eight notes and quarter notes that appear in the piece but are not overarched by a similar bracket, the notes will sound somewhat shorter.
Practically, two eight notes fit into a quarter note. But three eight notes overarched by a 3 will fit into an ordinary quarter note.
Normally a quarter note (1/4) equals to two eighth notes (1/8 + 1/8). But in triplets a quarter note (1/4) equals to three 1/12 notes (1/12 + 1/12 + 1/12) or (1/12 + 1/6), mathematically.