Someone can explain me what a checksum

Dear all

Happy new year!!!

I am getting GPS fix, using the RMC sentence.
At the end of the sentence, the is a checksum.

The mode is followd by a checksum and it's the only case where the two data are not separeted by a comma, but a star *.

For exemple, a mode can return 'A' and the cehcksum '*10'

I can not understan what is exactely a checsum. What it's more important for me, it's to undertand why, when my GPS return me that

32,171529.000,A,4613.197230,N,608.459615,E,0.00,335.79,060115,,E,A

the checksum is not shown/displayed?

Many thans for your help.

Cheers