There are two types of money in The Sims Mobile. There are simoleons and sim cash. Both kinds of money can be obtained for completing different actions in the game. Money doesn't grow on trees in this game, so the sims will have to work.
Simoleons are the money that you can use to buy furniture, clothes, hairstyles or accessories. You can obtain them for a hobby, work and special events. The amount depends on the duration of the event. Simoleons can be also acquired for watching ads.
Simoleons can also be exchanged for simcash, which is however not economically viable - the latter is much harder to obtain.
The cash is difficult to make during the gameplay. You get it for achieving experience levels, watching ads and completing missions. You can also buy simcash for real money. SimCash can buy you some house utilities, as well as clothes and hairstyles. It also allows you speed your sim up or create additional slots for new sims.