Final answer:
Mr. Gardiner outlines that Mr. Wickham is to provide Lydia with a settlement and his army promotion is key to their future livelihood, with no significant dowry from Lydia's family.
Step-by-step explanation:
The conditions for Lydia's marriage, as expressed by Mr. Gardiner to Mr. Bennet in Jane Austen's 'Pride and Prejudice', include that Mr. Wickham should settle a certain sum of money on Lydia, which would be her only provision in case of his death. Additionally, Wickham's promotion in the army is a consideration in securing their modest, but stable, livelihood. It's understood that the Bennet family would not be able to provide a substantial dowry, and so negotiations for the marriage are based on realistic and modest means without expecting much financial support from Lydia's family.