Hi. Maybe this will help for creating a tileable texture in Photoshop - if you have it of course.
Load your image. Use the offset tool (filter -> Other -> offset). this will essentially shift your image either horizontally or vertically so that you can see the seam that will occur if you were to tile it. Use the clone stamp tool (along with other tools (skew, warp etc) to "heal" the seam). Some textures, brick especially, will take a lot of time and practice to get right. A simple dirt texture though may not be so bad.
Hope it helps.