How do you offer tarpan during pitri paksh?

this answer presumes one has basic information about Hinduism and focusses on pitri tarpan not the dev tarpan.

in a vessel place sufficient amounts of water that you will use in the offering. to this (bucket or bowl of water add flower petals, white rice, black seasame seeds and tulsi leaves.

plant a shoot of the kus grass in the spot where you will offer the tarpan and make a loop knot at the top of the grass. make sure it is clean. now if you wear the janew thread, then you will need to remove it and wear it in the opposite direction that you usually do. (i.e wear it from right to left for this process and when you are done revert to usual)

wrap the end of you janew around your right thumb during the offering. (this is only for people that wear janew if you do not wear the janew then you can proceed by skipping this part of the instruction on the janew)

now facing the southern direction and standing in front the kus grass, cup both your palms and scoop up some of the tarpan mixture (water. rice, flowers, black till) in you palms.

The water should be poured onto the knotted part of the kus grass out through the right thumb and index finger by tilting your palms.

The first offering say "om krishnaayaa tripyaataam"

the 2nd " "om aryaamaa tripyaataam"

the 3rd " "om (say the name of the ancestor/s) pitraayaa tripyaataam"

the 4th offering " om sarva pitra tripyaataam" (say this mantra seven times and make seven offering to represent the 7 generations before you, now and after you)