What is signified by different kinds of crosses? For example some graves have club(cards game) leaves type edges crosses, some graves have simple crosses?
I think you are referring to the Budded Cross.
The article says,
A cross with three circles or discs on each arm in a Christian context represents the Holy Trinity but was probably also copied from earlier Celtic Druidry, where the circles or rings represent the three dominions of earth, sky and sea.
There are several names for this cross, depending on the interpretation. These include Budded, Apostles', or Cathedral Cross, all implying a religious theme, and Treflée or Botonée1 in a heraldic context.
And the Christian Cross, the best-known religious symbol of Christianity.
More crosses here on Wikipedia