A ramp is a surface that is sloped to make it easy for things with wheels to get between a low place and a higher place. The ramp in the photo is for people to get in and out of a truck.
Ramps are often used inside multi-storey car parks so cars can drive up to the top. Ramps are also used as well as stairs to get into a building. People can walk up stairs easily, but ramps are needed for people who are in a wheelchair, for people with prams, or for anyone who simply has trouble climbing stairs.