I've tried a few software programs for building family trees online. Each has it's pluses and minuses.
My favorite by far is MyHeritage.com. They offer free software you can download and then link up to their website. The great thing about them is they make suggestions of matching people in their database. I've found several missing family members this way. Now, I have also found mistakes, but that is why you have to verify and quantify your info.
Another great program is Ancestry.com. You have to pay for this access, but I find it well worth the price. You can research census records, military service, even old yearbooks! AND, you can directly save the information you find to the person in your tree it is for.
There are many other great programs for building your family tree. Check them out, see what has what you want to track for your family and which format you prefer. Ask people what they use and why.
But most importantly, start that tree!
Those fancy family fan charts look beautiful, but when you are starting out, can be intimidating.
You don't need a pretty diagram or a fancy program to start your family tree. When I began, I literally took a sheet of college-rule lined notebook paper. I wrote my information and drew an arrow to the left and an arrow to the right. Then I wrote what I knew about my parents. I then draw two arrows for each of them and wrote out what I knew about my grandparents. I continued this as far back as I could.
The next step is crucial!! Call up the people in your family and ask questions! You will have gaps in information or even in generations. You might be shocked to find out that your sister knows how your grandparents met due to a school project or that your mother has information on further generations back.
Really want to stretch your knowledge? Create a survey of sorts with questions about a person and their relatives and then send it out to all living relatives! Don't forget those cousins that live 1000 miles away!
It truly is as simple as this to get started on your family tree. If you enjoy this and get hooked, then look into how to organize your information.