Answer: You will need to clear out the existing plantings by digging them out by the roots or by using herbicide containing glyphosate to kill them (read and follow all of hte label directions), or in some cases you may be able to smother them.
To smother smaller weeds, cut them off short, cover with a thick layer of newspaper or cardboard, top that with several inches of organic mulch. By spring, you should be able to turn the soil (work in the paper and mulch as sources of organic matter) and then plant.
There is a chance the shrubs that were cut down will regrow next season from the left behind roots. The roots will also be in the way when you plant. Since you are going to replant the beds it would be helpful to have the stumps grubbed out (dug out and with an ax or saw cutting the main roots) or possibly pulled out.
You may find it more satisfying to concentrate on one bed at a time, leaving the others covered in mulch over paper so they look tidy in the meantime. Fall is a good time to plant, as is spring. August is not a good time to plant -- it is so hot and dry that the plants become stressed.
You may also want to look at a book or two about gardening to help you get started. The Dummies series, for example, includes several you might find helpful ranging from basic gardening to books on flowers, roses, bulbs, and landscaping.
Good luck with your project!
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