Onions are an easy crop for minimum effort. The easiest way to grow onions is from sets, which are tiny onion bulbs which have been treated to produce good bulbs. The treatment also reduces the possibility of the onion producing a flower and bolting. When growing onions, the best time to plant out is mid to late March or April, depending on the spring weather when the soil is a bit drier and warmer. You can buy onions suitable for planting out in the autumn and over wintering, provided that your plot is well drained, ideally with some added organic matter. As with all bulbs winter wet can cause the bulb to rot. To grow onions, the ground doesn't need to be really finely raked as it does for carrots and salad crops, just reasonable and not compacted.
I like growing onions, the taste of homegrown is good and they keep well so you can pick and use throughout the winter. Because onions are easy to grow, I know however poor the summer weather, and other veg crops may struggle, I can depend on onions to produce a good crop.
Provided you store onion sets somewhere dry and cool, you can also carry over spares to the next gardening season. Onion sets are often sold in quite large quantities, 50+ it is helpful to know they will keep from year to year.
video How to plant and grow onions and garlic