As seeing that there seems to be no good and right answer in regard of what "sharing merits" actually mean, my person thought of "sharing his merits" and let those possible to take, let be part. Not sure if the original questioner here has Nissaya (condition), to have even physical part on it.
Sharing merits does not mean, even if believed, that one can make a share of ones good deeds done, so that the fruit of it falls to the person he likes to give.
Beings are owner of THEIR action, heir of their actions...
So what one does to possible give other the chance to give causes for future good fruits, to gain also merits, is to let others be part on it.
This is made by either:
- inviting them to take part "come, join to..."
- tell them about done "yesterday I made Dana...", "I meditate 1h every day..."
- publish ones deeds of merits
- give talks on merits
- act meritorious, so that others may see
...and so on.
What ever being has one one hand the "physical Nissaya (condition)", means get physical in touch of it, and the "mental Nissaya", means capable to receive it by heart, is touched by it, takes in that way, mental, or physical and mental part on it, with joy, rejoices with it, has gained a share on your merits.
A being not in the physical (incl. fine physical/material) or mental, or both, condition, can never take part on your merits.
That means that a person, not attentive for good deeds, not seeing the gain you accumulate, or accumulated, sees no value, will not have the possibility to take on your given oppotunity.
Your gain on dedicating, sharing merits, let other take part, conteracts your greed in regard you merits and is anyhow an additional gain for you.
Especially when sharing merits where being are not attentive, even aversive of good deeds, in bearing critic, losing reputation under them, set you out to be criticised to like to lift your self..., all this giving up of wordily reputations, are reason for additional merits.
Having gained, heard, seen about good deeds, and knowing the joy ofhaving part on such, you like, out of compassion, out of sympathy, other have the same possibility.
You are optimistic that other being had made merits in the past, so that they are able to take your gift. If they have have Nissaya with the Dhamma, Upanissaya (strong condition, karmic "destiny" with you and words of wise) who knows?
On places where being are gathering who strongly seek after gross food and have never enough, in the peta-realm or in internet (to give a graspable sample), its difficult to share merits. Beings are to much focused on gross food, signs, sounds... knowledge, ideas, fine material gain and reputation.
That's way aside of knowledge, such as sharing merits, approving, expressions of joy, mudita... is seldom seen. Sharing merits goes agains business, gain and consuming and liberates.
Joy is one of the pre-conditions for concentration, joy with what is worthy to rejoice with it, the condition for right concentration and this the condition for liberation. Without right joy, no progress on the path.
May the merits done by me here, benefit all being, may those capable to rejoice with it, gain highes concentrations, path and fruits, with support of it, may the Devas inform those who could not see or hear from it.
(Note: This is a gift of Dhamma and not meant for use of commercial purposes and other wordily gains but intended and bound to awakening and liberation, and so good shared.)