If you’re interesting in researching and building your family tree online (the only place to do it!), but can’t justify the cost of ancestry.com or other commercial sites, I recommend you take a good look at https://familysearch.org, which is 100% free as far as I can tell, thank you Mormons!
Unlike Ancestry, when you go to add another person to your tree in FamilySearch, it actively attempts to find a match for that individual for you in its existing database of millions (billions?) of people. If you decide that none of the matches are the person you want to add, then you can go ahead and add them, in the knowledge that you are creating a brand new entry, with a unique ID, for that person in their database. So don’t do it lightly!
Ancestry will let you add a new person very easily, with no cross-checking with the trees of other members. Sure, it provides an excellent hint system for you to match your ancestors with those of others, but this happens after the event, i.e. after you’ve already added that person to you personal family tree. Which means that there is likely a much larger amount of data duplication and errors in Ancestry compared with FamilySearch.