Can anyone help me with my Government and Politics A-Level query?

I am doing my course via correspondance, so no teacher to ask. If you can explain this passage, taken from the course materials, about Proportional Representation I would be very grateful:

” There are multi-member constituancies in which seats are obtained by ‘quota’, i.e. that proportion of votes neccessary to secure the election of a candidate. For example, in a two-member constituancy, the quota must be one more than a third of the votes. Hence the quota is calculated by dividing the total number of votes polled by the total number of seats to be filled plus one. ”

Thank you if you even try to explain.