Experience is the most important element of the game - it represents your progress, allows you to buy abilities and upgrades for your workshop which in turn gives you new options and orders. Each mounted or dismounted part gives you +1 point (this doesn't apply to separating parts from each other [wheel-tire] and changing oil), regardless of difficulty of its installation. Examining each part also gives you points. However, these methods are very slow and you shouldn't rely on them if you want to develop your character quickly.
Orders give you more than 100 experience points. Difficulty of an order has no real impact on experience - reconstructing an engine and changing filters gives you a similar amount of points. The only difference is in how much money you get.
Abilities and expanding workshop
When you get new levels, by completing orders, you can use one ability point and spend it on an upgrade. The list of available upgrades can be checked when you interact with the toolbox that can be found in your garage. Abilities are connected with each other (if you want to, e.g. unlock faster parts examining level 3 you must unlock the previous two levels first). New columns with icons representing upgrades are available only after getting a new level (check the numbers in the bar next to columns at the bottom). Abilities can be reset at any moment without any consequences!
Limits for new columns can quickly become rather high which means that there is no pattern which upgrades you should select first - after a while you will have two / three unlocked icons. Besides player abilities and expanding your workshop you can also unlock a few tools such as electrical meter or tablet. Measuring equipment can be used for, e.g. diagnosing elements of electrical system or checking pressure in cylinders. The tab, that allows you to select tools, is available in repair mode and can be selected from the quick menu.