That's one of my favorite topics. However, my experience is with produce/crops grown in a very hot and humid sub-tropical climate and probably doesn't apply much to Finland.
Because my climate is so demanding, my primary method of storing excess veggies is canning. Potatoes, carrots, green beans, beets, okra, peppers, peas, various beans, tomatoes, and others the excess is usually canned. Excess Corn is usually frozen, but we love fresh corn so much I make three staggered plantings starting about April 1 to provide a continuous supply of fresh sweet most of the summer. Also, we freeze some okra, jalapenos, and bell peppers.
Onions and garlic are stored in an outside covered shed which is open on three sides for ventilation. I also store potatoes in a dark place in my well house which tends to be somewhat cooler (cooler than 100 deg.F). Potatoes stored that way are primarily used for seed potatoes as in my location I can get a spring and a fall crop.
The main prepping I do for storage is on onions. I grow in excess of 200 pounds of yellow and red onions each year harvesting in May, planting in Nov. To prepare them for storage, I withdraw all watering at least one week prior to harvest. The pulled onions are left to dry in full sun for 1-2 days depending on the moisture levels. Then the tops are removed, and they go into storage. Pretty much the same for garlic only I don't dry them in sunlight but in a shaded area.
We are able to use our garden to produce over 90% of the veggies we consume and as much as possible consume most of it fresh by using multiple crops and staggered plantings. Canning works well but the taste of fresh is still tops in my book.
, carrots
, beetroots etc for the winter? 
it worked ok, but had to put shelter over it because of the rain.