I received the request to make a project with Indesign. 300px width 100px height.
This project should have the crop marks on the corners.
Questions: 1) If I want to have those crop marks, should I create the project of the exact width that I was requested (300x100) or it should be bigger? 2) If it should be bigger, how much bigger should the project be?
You set up your document exactly to the trim size (the size requested). When printing/exporting the document, you check "crop marks" in the "marks and bleed" section of the print/export dialog. ( reference: Adobe Help Docs )
As a general rule, you should always set your document to the final desired "trim size" and then worry about what size paper you will print on later. In almost all cases your printed item will be printed on media that has little relation to the size of the finished item (e.g. a business card is printed 8 to a sheet aka "8-up")
Just want to add to/clarify Yorik's answer. Crop marks and bleed marks are different. If the final product is full bleed (illustration and background color go off the edges of the paper), the way I would set up is (in Document set up)
When exporting, check crop marks only (you don't need to check bleed marks), and make sure you also check the box for "use document's bleed settings).
This will allow for trimming errors, i.e. white edges or trimmed to smaller size.
What he said^^. It generally pays to know what the required bleed size is though rather than just using an arbitrary amount e.g. 10-20px. Bleed sizes are commonly 2mm, 3mm or 5mm.
