Having been born at the beginning of the Space Age, my memories of the first missions are vague and scant, though the names are all familiar.
This was the first human spaceflight with Yuri Gagarin on April 12, 1961. It was a single (and the shortest ever) orbit of earth. Many of the details weren't known for years because of the secrecy of the Soviet space program, but Gagarin apparently landed safely by parachute separately from the spacecraft.
Also in this series is Sputnik 1, the first artificial satellite, which went into orbit in 1957 and is considered to have been the start of the space race between the USSR and USA.
This one shows the 'interplanetary exploration'
I am rather fond of this stamp celebrating the first man on the moon that comes from Guinea and shows a view taken from the moon's surface towards earth, with Africa in prominent position.
and while we are on the topic of views of earth from space, may I take this opportunity to remind you of the excellent daily photos from the ISS by Chris Hadfield.