It is cards.length(), not cards.length (length is a method of java.lang.String, not an attribute).
It is System.out (capital 's'), not system.out. See java.lang.System.
It is
for(int a = 0, b = 1; a
not
for(int a = 0, b = 1; a
Syntactically, it is if(rank == cards.substring(a,b)){, not if(rank===cards.substring(a,b){ (double equals, not triple equals; missing closing parenthesis), but to compare if two Strings are equal you need to use equals(): if(rank.equals(cards.substring(a,b))){
You should probably consider downloading Eclipse, which is an integrated development environment (not only) for Java development. Eclipse shows you the errors while you type and also provides help in fixing these. This makes it much easier to get started with Java development.