If your planting area is covered with grass or weeds, you will have to totally eliminate them. There are 2 possible methods for this:

Requirements

√ Grass Killer
√ Rake
√ Flat Spade
√ Newspaper
√ Tiller or spade & Fork
√ Mulch
√ Organic Materials

Chemicals Based Method

If you are in a hurry or have a large area to cover, this method will help.

Get grass killers at your garden center. Be careful to closely follow all the directions and instructions clearly detailed on the label.

Spray all the grass and weeds inside the bed area, but be careful not to spray outside of it as it would kill the grass or plants that you didn’t intend to get rid of!

Let the area alone for 72 hours at least.

Rake away the dead grass and weeds.

Non chemical Based Method

The fastest, but backbreaking way of doing it is to use a sharp flat spade to dig out grass and weeds. Ensure you have removed all the roots of the weeds or they may grow back! A slower method would consist in smothering grass and weeds using layers of newspaper (9 or 10 pages) that you would cover with piles of mulch. But this process will take several months. As an example, it should be started in the fall for planting the following spring.