Jobs is the second tab in the game, unlocked after Q-Bae informs you that you need to raise money to pay for Nimh's refund. Performing the various jobs accessed through this tab is the sole source of money in the game, used primarily to buy gifts and take guys on dates, but also serving as a gate to advancing relationships.
Initially, only Seamstress is available, but every job can be unlocked once you meet its skill requirements (skills being earned through performing hobbies). Performing a job multiple times will unlock promotions, increasing the pay per completion.
The only exception to this is the job "Mystery Solver" which is available immediately once the Cole DLC is purchased and cannot be earned.
For Crush Crush Jobs, see here.
Note: Data values are based on 1.0x multiplier and calculated within .5% error. Values have been rounded to the nearest whole numbers.