What can I expect if I tear?

Depends on degree. If the question is in reference to a vaginal delivery, it depends on the location and extent of the tear or laceration. The results may range from none or few symptoms to pain requiring medication, and problems with bowel continence, and pain with intercourse. The latter items are not likely, but they cannot be predicted in advance, nor can the degree of tearing.
Sore bottom. Small tears are very common, especially with a first baby. Most women require a few stitches. Larger tears may require stitches in the muscles of the pelvic floor or around the anus. These repairs heal very quickly and by the 6 week postpartum visit they typically look good as new. You may need stool softeners if you have a large tear and expect a sore bottom for a few days to a few weeks.