When we say weekly reports, Meaning you have to pass your work on weekly basis. For example you joined Facebook Campaign and it requires you to share 5 posts per week. Let say you completed that already and will past weekly reports now, this is an example of weekly reports

*Facebook Campaign*
Week 1(Indicate the date of week 1, like march 02-march 08)
Link of shares.
1. post your shared links here
2. post your shared links here
3. post your shared links here
4. post your shared links here
5. post your shared links here

Something like that. You just have to send what were campaigns were asking. just read their rules
Note: Some campaigns has it own format on passing weekly reports, just follow the format.