To apply a texture to a vector in Adobe Illustrator follow these steps:
1. In Adobe Illustrator, add whatever background you would like to use and then lock the layer. We won’t be touching this for the rest of the tutorial.
2. Switch to Adobe Photoshop and paint the texture you would like onto the canvas with a brush stroke (or other method).
3. Make sure that you disable visibility for the background layer. We are going to be exporting this texture as a transparent PNG.
4. To export the texture go to File>Export>Export As
Make sure the Transparency box is ticked. Export the transparent PNG (preferably at a high resolution)
5. Go back to Adobe Illustrator and add the newly exported PNG as it’s own layer.
6. Add your vector onto a new layer on top of the PNG. Make sure that this vector is a compound path before you continue.
7. Select the vector and the PNG (the vector MUST be on top), right click and select Make Clipping Mask.
8. To adjust the position of the texture, drill down into the clip group and select it individually as shown.