How do I make the Minecarts active?

The minecarts are all broken. Seems like they are pretty useful for fast traveling between some places around the city, farm and mines.

How do I make these work?

Once you complete the Boiler Room bundle, the minecarts will be repaired and you'll have access to fast-travel between the Bus Stop, Mines, Town, and Quarry (once that's unlocked).

Complete the Boiler Room bundles at the community centre. The boiler room itself is unlocked by completing two bundles from a previous set- the pantry or craft room bundles are the easiest for this.

Alternatively, if you have a Joja Corp membership, pay 15000g at JojaMart using the Community Development Form.