Red River Valley is a beginner tab. It's a well known folk song. The notes are not hard.
There are two aspects that make it a little challenging.
1. The counting, to be accurate, requires holding notes for several counts, or beats.
2. The tune is repeated an octave higher.
Here's a brief discussion of these two challenges.
1. The feel of the song, for me, is a slow two. But, when I'm teaching it, I count it in four. Each descending stem gets one count. The circled fingering numbers get two counts. A fingering number that is circled and dotted gets three counts. A number that is circled and has no stem gets four counts.
Some of the notes are longer because of the ties. That's the curved line that goes from one finger number to the same finger number. This notation system only intends to make the counting completely accurate.
The first such indication is in the third full bar. (The very first bar with two notes is not a full bar.) The third finger note, a C on the G string, gets five counts. They way to count it accurately is to start on the second beat where it begins: two, three, four, one, two.
We keep repeating our count of four constantly. In the seventh bar the note gets four counts and ties to the same note getting two counts.
Fortunately, the song is well known and can almost be played with sufficient accuracy by feel alone. And perhaps some beginning to intermediate fiddlers could easily play by heart and just nail it.
2. Repeating the song an octave higher creates additional interest. It also doubles the learning time and effort. You might as well consider you are learning two tunes.
But this device of playing a tune an octave higher or lower is used commonly. One of the members of our local fiddle group, the Bay Area Fiddlers Association, will play some tunes an octave lower than the rest of us, as a variation.
Getting used to the changes in fingering that must be done to accomplish this trick is part of the gain in expertise on your way to mastery.