To fix the FILTER-HOLDER onto your lens you need an adaptor ring.
Then you slide your filters into the holder ... so' easy.

There are 3 different Series in the COKIN System.
Basically, the size to be used depends on the outer diameter of your lens :
the larger it is, the larger the holder you must go to.
1) « A » Series : for lens diameters from UP to Ø62mm
2) « P » Series : for lens diameters from Ø48mm to Ø82mm
3) « X-PRO » Series : for lens diameters from Ø62mm to Ø118mm