Hi there accounting-daute,
It's vital that all your transactions be entered correctly for your books to be well balanced. QuickBooks Online is a great tool able to help you keep track of sales and expenses in order to be able to see the profit of your business. I can provide some information about keeping track of the costs of certain jobs.
While there isn't the same exact job costing feature as QuickBooks Desktop, in QuickBooks Online Plus and Advanced you can keep track of Projects. You can associate a project to a customer to be able to associate expenses and sales relating to this job. You can view some information about projects by clicking on the article I linked earlier in the paragraph.
if you have any other questions, feel free to reach out here.