Depends on size. You might not feel anything if it's small. Otherwise, it could feel like a lump, a node and if it's big enough, it can feel like a growth/mass on your neck. If it's liquid, like a cyst, it could be soft. If it's a solid growth, it could be rubbery and if it's calcified, it could have a rock/hard feel to it.
Maybe nothing. Unless it's a very large nodule, most patients don't really feel them. Many are incidental findings with a physical exam or imaging study which includes the neck. If any symptoms are felt, they might include: mild neck pressure and/or swallowing discomfort. Sometimes, if large enough in a person with a thin neck, you may be able to see a bump over the thyroid location in the front of the neck.