SYSPRINT: All system output will appear under this DD card. Suppose you are copying a VSAM file using IDCAMS. Then, number of records processed, highest condition code etc.. will appear under sysprint. You cannot customise SYSPRINT output.
SYSIN: This is nothing but SYStem INstruction. Suppose, you want to sort a file on certain key. You have to have following command under SYSIN.
SORT FIELDS = (starting-col,length,data-type,A/D)
SUM FIELDS = NONE
DUMMY: Mainly used where user is intended to simulate a program without creating an output file.