Proportional representation- votes are counted nationally and divided proportionally among the parties, so a party with 40% of the votes, gets 40% of the seats.
First past the post- each area is separate and the votes only count for that area, so if you come second, you lose. In theory, a party could have 40% of the votes over the whole country, but no seats because they have lost in each area.
There's also AV, alternative voting, where you have a first choice and a second choice and if no one gets a clear majority, the second choice votes are added.
- For Teachers