It must be an advertisement soliciting the participation and contribution of programmers writing actual source code. This is not intended as a general purpose ad for consumer products which just happen to be open source. It's for finding programmers who will help contribute code or other programmery things (documentation, code review, bug fixes, etc.).
Your ad should be an original creation which has not previously appeared on Stack Overflow. Please do not resubmit entries that have appeared as ads on Stack Overflow in previous periods.
as I understood that I can actually create and advertisement for a project that I like (but I am not a creator of this project), and is an open source. Am I correct?
By I am not a creator I mean - I am not a creator, contributor, have no connection to neither creator nor any of the contributors. It just happened that I found the project and think that it is amazing.