im making a gun and i have the model and the textures done but i dont know how i can open the texture of the gun into the maya project...

Go to Window > Rendering Editors > Hypershade. Then click on the Phong button on the left. If the Attribute editor isn't open already, then click on the new Phong material and do CTRL+A. Then where it says Color, to the right there should be a little square with a triangle that is shaded in pointing into it. Click it and then click on File. Then click the little folder that shows up on the right across from Image Name and direct it to your image. You will probably want to rename the material so just click on the material you just made and in the Attribute Editor you can rename it where it says "phong:" then hit Enter after typing in the new name.
Reference Image: http://prntscr.com/3rg5sr