What does Lamarckism idea of “acquired traits” propose?

Acquired Traits of the parents are directly passed to their offspring.
Lamarckism proposes that traits gained by the parents during development will be passed directly to their offspring.
In a very simplistic form it would mean that the musculature gained through weight training would directly translate to any offspring fathered by a weightlifter.
An example used in Lamarckism is that since giraffes needed to stretch their necks upward to feed on the leaves of taller Eucalyptus trees their offspring would be born with longer necks.
This allowed for traits to change in each successive generation. Making evolution fit within the time frame of Archbishop Ushers time frame for the development of the life on earth of beginning in 4004BC.