You can buy two types of software that will help you with your search and tree-building.
The first is software that you install on your computer. Most of this type of software helps with your storing, organizing and displaying information of your family tree. Which is a great help if your paper tree grows and becomes difficult in keeping it organized. One of my personal favourites is Family Tree Maker which is now owned by ancestry.com
The second are online tools that will help you tracking down members of your family. Some are very basic, some are more sophisticated.
Although a professional genealogist will give you much more information to go by, this software helps you to find the right course so you can fill in your tree.
When you decide to buy some software to help you with your project, keep in mind that the quality of it may vary. It is advisable to search for reviews of your favorite programs on the Internet, and also read what other users say about it. The choice you make then is an informed one and you know what you’ll get for your money.
You can use additional help for your tree, especially if you want to go as far back in history as possible.
These tools will not only help you with that, but also with organizing and time-managing your project, so you still will have fun going on with it.
Good luck with tracking down your ancestors and building a tree you can pass on to the next generation!