That register is just setting a bunch of bits in it. The + is essentially an OR in this case. The statement can be rewritten as:
TACCTL2 = CAP | SCS | CCIS1 | CM_1;
The info for each #define (CAP, SCS, CCIS1, and CM_1) should be in the libraries you are using. bits they set are shown on page 372 of the doc you linked.
CM_1 for example indicates capturing on the rising edge.