Preface: all of the following comments are meant to be constructive.
Given the lighting, ISO, and shutter speed, it's clear that it wasn't sunniest of days to go out shooting. In the future, especially when shooting fast-moving subjects like squirrels, make your life easier by going out on a day when there's plenty of ambient light, so you won't have to slow your shutter speed (blurring movement) and raise your ISO (reducing fine detail). On that note...
Your photo is out of focus, in two ways. First, the lens is focused on the tree bark instead of the squirrel. Don't know if the squirrel was sitting still or not, but when shooting a fast-moving subject, it's good to take multiples before reviewing your images, trying to nail the focus in each one. This gives you some insurance (i.e. more photos of the same thing to pick and choose from), which is important because proper focus is not guaranteed, nor is the opportunity to get the same shot again. Checking each shot for composition/etc immediately after taking it is a good way to miss something.
Second, the whole photo is fuzzy, indicating hand shake/movement. It may be hard to see when zoomed out to half size, but blurriness makes a difference, especially when you need to crop something, which would have benefited this shot (imo). It's exacerbated by the high(ish) ISO. When shooting, especially when zoomed in, it's important to be as still as possible before/while hitting the shutter release. This can be mitigated by image stabilization, but that can only do so much to compensate for shaky hands and/or body movement.
Lastly, when shooting moving subjects, you'll want to keep your shutter speed somewhat high, or movement will be blurred. Bare minimum (for me) is 1/125 s, and that still depends on the subject (and focal length etc). Squirrels, for instance, can be pretty jittery even when they aren't moving around. Again, more ambient light will let you speed up the shutter.
It's said that it takes 10,000 hours to become an expert at something, so you're off to a good start.

Keep at it!