Probability notation. What do "4c3" and "4c4" mean

4 fair coins are flipped. What is the probability that at least 3 of them come up heads?

P(H = 3, T = 1) + P(H = 4, T = 0)
= (4C3) * (1/2)^3 * (1/2) + (4C4) * (1/2)^4
= 4 * 1/16 + 1 * 1/16
= 5/16

What do 4c3 and 4c4 mean? How do I use them to get 5/16?

4c3 means "from 4 choose 3"
4c4 means "from 4 choose 4"

you can find both with a decent calculator