You can import clothing you have made from other 3D software into Unity. Recommended formats are FBX or OBJ; if you are importing skinning (weighting) information, we recommend using .FBX, however .Blend and .DAE will import skinning data as well.
There are a couple of ways you can import your clothing file. You can either drag and drop the file into your project window from where you have saved it, or, you can go to the top menu, click on Assets>Import New Asset and choose the obj file from where you have saved it.
This will put the obj file into your main Assets folder. You can create a new folder for the item by right clicking in the Assets folder, and choosing Create>Folder.