NCAA divides most of its sports into three divisions: Division 1 (D1), Division 2 (D2), and Division 3 (D3). Divisions have been put in place to level the playing field by pairing similar sized programs in competition. Every school chooses what division it wants to play in, but must meet specific NCAA division standards and generally must play in the same division for all sports. Most athletes and their families are familiar with D1 sports because those are usually televised. However, only a very small percentage of high school athletes will play at the D1 level - in football, only 1 in 100 high school players actually play D1 football. Playing football at any level is actually mostly similar, but different divisions will lead to some different experiences. You should know the differences between the divisions if you are going through the recruiting process.
While there are clear differences in the average school in each division, there is significant overlap between the top of each division and the bottom of the next division up. In every category, the experience at top schools in one division is similar to an average school the next division up, and the bottom schools in each division are similar to an average school the next division down.