How to plan a menu
If you're a beginner at planning menus, I might suggest taking it one week at a time. If you want to go to the store less often, you can work up to two weeks when you have it down.
Also, if you're feeling overwhelmed, remember that you don't have to plan every little thing. I usually only plan the main dish for dinner. We just keep breakfast stuff around, and lunch is usually leftovers from dinner. As for side dishes, I do write some down sometimes, but usually I just pull out a bag of frozen veggies or something similar.
How to plan your weekly menu and shopping list
Keep a list on your fridge. Any time you run out of something, or notice that it's getting low, put it on the list.
The day before you go to the store, look in your fridge. What's there that needs to be used up? Have these things in mind, or make a list if you can't remember them all.
Now sit down with your list of stuff that needs to be used up and a cookbook, or your recipe box, or your internet bookmark list of recipes you want to try, or all three. Also get your weekly schedule. This will help you see if you need to use the crockpot one day because you will be gone the hour before dinner, etc.
Now plan your menu! Make sure you use up the items in your fridge that need to be used. After that, you can try family favorites or something new. I try to plan two or three really easy meals per week, for days that end up being busier than planned. As you write down your menu, look at each recipe. Add any items that you will need to your shopping list.
When I'm done, I like to categorize my shopping list. It's rather overwhelming to walk into the store with a fifty-item shopping list. It's hard to find what you need. Instead, I sort it by categories: produce, deli, dairy, frozen, etc. This helps things to go much better at the store, especially if you're shopping with small children.