Everything is very simple. Each company has its own rules, but in general they are similar. For clarity, usually the bounty manager himself gives an example of how to properly do a report. Also, by browsing the topic, you can see examples, just like other bounty companies do. Mainly follow the deadlines for submitting reports. Here is an example of a report in the facebook bounty:

Campaign : Facebook
Bitcointalk Username: Biligma
Spreadsheet No: 425
Facebook Account: https://www.facebook.com/biligma.sugarova
Week#: 2
Links:
1. https://www.facebook.com/biligma.sugarova/posts/172684790215083
2. https://www.facebook.com/biligma.sugarova/posts/172729430210619
3. https://www.facebook.com/biligma.sugarova/posts/172766716873557
4. https://www.facebook.com/biligma.sugarova/posts/172900873526808