2cm dilated,what does contractions feel like??

went to my appt she told me I was 2cm dilating and my liner thing is thining and she sent me to get and ultrasound to check for fluid and growth and put me on a monitor. after 3hrs of nervousness, being scared and crying.. they sent me home after my heart rate went down.. finally sent me home and sense it's my first I think my mucus plug is slowly coming out it was brownish stringy type looking but I don't know what to look after that I don't kno what contraction feel like or what my water braking looks like etc..