Muhammad,
Maybe you need to re-phrase your question, but anyway to give you an idea on relationships and lags
Types of relationship in a Precedence Method
Finish to Start Relationship [[[[[[[1st[[[[[[[[[[F ---->S[[[[[[[[2nd[[[[[[[[[[ (2nd activity can only start when 1st activity is finished) now you can put a lag (+/-) and it would mean 2nd activity can only start (if you put 2 days lag) 2 days after 1st activity is finished
Start to Start Relationship S[[[[[[[[1st[[[[[[[[[[ --->S[[[[[[[2nd[[[[[[[[[[ ( 2nd activity can start in parallel with 1st activity) if you put a lag of 6 days then 2nd activity can only start 6 days after the start of 1st activity
Finish to Finish Relationship [[[[[[[1st[[[[[[[[[[[F ----> [[[[[[[2nd[[[[[[[[[F (1st activity must finish before 2nd activity can finished. if you put a lag FF with 1 day lag, the 2nd activity will finished 1 day after 1st activity is finished.
Start to Finish Relationship S[[[[[[1st[[[[[[[[[ [[[[[[[2nd[[[[[[[[[[F (1st activity must start before 2nd activity can finished)
Best regards,
Daniel