Like MeowZedong said, it may be an eighth note rest. But it's hard to tell from your description alone. Fortunately they provided an image for reference.
Also, sorry to sound like a "dad" here and give you advice you didnโt ask for, but if you are just now starting to learn to read sheet music I wouldn't recommend a sink or swim approach of taking music and learning it.
If you already know how to read sheet music and you aren't new to it then ignore the rest of this
unprompted advice warning
I would get a solid grasp of fundamentals first and then try to have fun with music that is suited for your level. Get a metronome (always practice with a metronome) and a graded skill book for your instrument like
Or
(It doesn't have to be those particular ones, they're just examples for piano) and work through the exercises with the metronome. Do each exercise slowly at first, so slow that it's painfully comfortable. Repeat a few times, then increase the BPM on the metronome by 5 or so and play the same piece again multiple times. Only increase the BPM when you nail it at the current pace.
Perfect practice makes perfect
It will be boring at times, but a book like that (and the practice methodology) ensures you cover all the basics and it introduces everything you will need to know as you need to know it. Its about building up muscle memory and linking it to the visual ques from the sheet music at a good pace of learning.
Those books also have songs in them that are suited for the skill level so you can have some fun. At the end of your practice session you can then try to work on a peice you really want to play. Like the one you linked. But make sure the focus is on those fundentals and the book lessons.
You can also do ear training which is more free form and like sink or swim. Without reading music, try to repeat a peice from a recording by just listening to it. This will be a different form of practice than sheet music, its practicing different skills. So it can be supplemental if it interests you.
