Nice sedum in that photo.
1. Contact the utility companies to find out where everything underground is. It is a free service, and they will mark exactly where the utilities run under ground (power, sewer, water, gas, etc).
2. Once you have that information I would start by removing all of the landscaping fabric. As you can see the weeds just grow right through it and make it even more difficult to weed, plant, etc.
3. You have options at this point. Do you want to use some type of wood, brick, stone, cinder blocks? Once you have determined what you will use, you can make a shallow trench to hold the low wall in place. Add compost to make the planting area level and start adding plants. You will be able to dig once you know where all your underground utilities are.
By the way, I love your avatar.
