@mary15 You just say at the start of every day:
Jesus, I unite all my pain/struggles/torture with Your pain, suffering and death on the cross and I unite it with all Masses that are offered today and I offer it to You Jesus through hands of Blessed Virgin Mary for… (intentions). Amen.
Because our prayers aren’t perfect and will never be but offering it with Blessed Virgin Mary is different, Mary is our advocate and She knows how our prayers could be better offered. She always prays for us if we ask Her to do it. When we offer something to God by Mary She offers it in more better and perfect way.
When we unite our pain with Jesus’s pain it becomes meaningful. Our sufferings is never in vain but our pain etc. can become useless if we don’t use it in right way, for example if we don’t accept it or we blame God for our pain, or if we protest against it. Our suffering alone is not enough to change anything but united with Jesus we “cooperate” with Jesus’s plan for us. When we unite our pain with Jesus we accept His will for us in our tribulations.
God always hears all our prayers in any form. Uniting with all Masses offered that day means also to accept and to offer it to God in more perfect and humble way. Our prayers become “stronger”, “better”, “more perfect”, when we offer something to God united with prayers of Church, Mass, we participate in unity with others and share graces of it through it.
I am speaking from advices I’ve been given.