In the following examples, I will attempt to explain how I painted the grapevine above.

1. Create a round 2D path with a diagonal gradient of dark and light purples. Change path object to an image. Use burn tool to shade grape to give it a painted and rounded look. Save as an object if you will want to use again.
2. Resize individual grape according to the size bunch of grapes you want. Duplicate and place grapes using the order tool to move them back or forward until the bunch looks pleasing to you. With one of the grapes selected, right click, select   all and merge as a single object. You can save the bunch as an object if you   like at this point.
3. Create a 2D custom shape, leaf 4 with the path tool using dark and light green  diagonal gradient in the shades you prefer.
4. To make it look more like an actual grape leaf, use path edit to change the shape. Or if you like, try creating a leaf with the spline tool. Once again, convert path  to image and use the burn tool to shade. Using a basic brush and black or a very  dark green, paint on some veins. Now you can use the smudge tool or water drop brush  to do a little shading until you are happy with the leaf. Remember, you will probably  reduce the size of the leaf once it is finished to use with your bunch of grapes and  a vine so the shading and shape is not quite as important as it would be if you wanted  a large one.
5. Using a basic brush with size set to about 10-12 in a medium brown set to the 2 color option in the brush panel and brush mode set to paint as object, draw a freehand vine with several branches. With size set to about 4-6, make some curlyques in a few places, then to give it a little definition, paint on edges in black with brush   size set at about 2.
6. Now put it all together, duplicating and resizing grape bunch, leaves, etc. until  you get the look you want. Add more curlyques if you think they are needed. Merge  as a single object. Save as an object to your easy palette for future use. Add a  shadow if desired.