I just happened to be doing strawberries yesterday so my tutorial is showing strawberries, but you can do this with any vegetable, fruit or even prepared foods like meatballs or chicken fingers.
Step 1: Have extra. I buy a lot of fruit and veggies when they are "reduced for quick sale". This offer will vary by grocery store but most places have a section where they have dying produce and can be substantially cheaper. With these strawberries, for example, there was one squished one in the bottom so it was marked down. Pick out the yucky bits, this means anything that you can't or won't eat and wash the rest of the food. Wash and dry the food like you would before you would eat it fresh.
Step 2: Prepare. If you had smaller berries you do not need to cut them, if you want frozen whole berries you do not need to cur them either. Personally I like the green strawberry tips removed and then cut into quarters so they fit in the blender nicely (I use them to make smoothies). You might want to cut your pieces so they are the right size for whatever meal you are thinking of or a smaller generic size or even leave things whole. This is personal preference. When you are done cutting everything to size place everything on a single layer on a baking sheet. If you are afraid of the food sticking to the sheet you can use parchment paper or freezer paper as a liner but I have found that I do not need the paper if there is no access water from the wash.
Step 3: Freeze this layer of food.
Step 4: After it is frozen, remove the items to a bag and enjoy your frozen foods.
Note: You don't have to do a lot at a time. This large bag of strawberries started out small. I found that my family was not eating a large box of strawberries before they went bad so I would freeze the left overs before they were no longer edible and, on top of buying them discounted when I saw it at the store, it added up to the large bag pictured.
This also works great with discounted meats. I put meat frozen in this manner in bags and then can just take out what I need. I have lots of different cuts of meat and chicken in the freezer and just grab what I need.
My family also has pizza every Friday and sometimes we like different toppings. A whole can of olives or a whole pepper or even a whole package of sausage is too much for one or even two pizzas so I freeze the left over toppings in this manner. Toppings can then be added to the pizza frozen and are defrosted while cooking.
As an example on how you can cook using frozen ingredients, the other day I made soup using frozen cooked, chopped, chicken thighs and frozen cooked, chopped, sausages. I took a handful of both meats and put them in a pot with a little margarine and some garlic. when the meat was slightly defrosted I added handfuls of different veggies from the freezer and added fresh chopped potato (Because I had none frozen). Covered the whole thing in chicken stock, seasoned it, and let it simmer for about 20 minutes. No one knew it was frozen stuff. Good as new!
Another time I will give tips about freezing whole meals ahead. Hope you found this helpful!