different plants are planted at different times. So it isn't really a matter of planting a whole garden at a given time.
The first thing to do is find out what USDA
growing zone you are located in.
Then find out when your last frost date is for that area.
You also need to take a soil test before you start planting. Different types of plants need different types of soils.
Also you need to watch your garden area for a few days so you know how much sun the area or areas get. Different plants have different light requirements.
Plan on starting your plants and
seeds that can not handle frosts about two weeks after that. And pretty much work from there. Most
seed packets will tell you when to plant according to that frost date.
If you buy live plants remember you should quarentee them for awhile before you let them near your other plants so if they have a disease/pest you don't spread the contagian.
Also remember it is necessary to harden off plants before you plant them outside.
Also some plants will need a trellis or stakes and you need to know that in advance because you don't want to be putting those aids in after the plant has developed roots. So you don't accidently damage the roots.