You can use blueprint to make part. Part is used to strengthen your unit (tank, troops etc)

How do I get blueprints for making parts?

You can Get blueprints by progressing through Campaign Missions. Supplies earned from AFK also sometimes contain blueprints.

How to use blueprint to make part?

Click unit > blueprints (bottom) > choos blueprint. You need materials and components to make part.

How to obtain materials ?

You can get materials by disassembling parts. Go to the Engineering Center > Disassemble.

Casting component, electronic component, machining components, precision component, stamping component, chemical raw material, light industry material.