I can only sell batteries, how do I produce and sell other things?

You need to upgrade your factory. Selecting your current building, select the arrow tab and select 'upgrade'. If you go back to the other tab for that building, it will show you the other items you can build and what level is required to build them.

You can also making two other types of buildings. Your first building is a Material Workshop.

There are also Processing Workshops and Packaging Workshops. They cost different amounts of money to construct.

Material Workshops can make: Battery Cell, Screen Diode, Circuit Unit and Processing Unit.

Processing workshops build lithium batteries by default. Upgrading them can unlock Mobile Phone Screen, Mobile Phone, Monitor, Large Power Supply and Handheld Device Display.

Packaging Workshops make PC Motherboards by default, and you can unlock PC Base Unit, Personal Computer, Handheld Device Motherboard and Handheld Gaming Console.

You can make multiples of each type of building. The two higher-up buildings all use materials you have manufactured in the material workshop or one of the other workshops.