Raspberries spread quickly. A few plants will be many plants in a couple years.
Traditional raspberries will only bear fruit on last year's canes. Everbearing raspberries will produce two crops. I have both kinds. My traditional crop comes on in early summer. As it winds down my everbearing start producing. I really love the golden raspberries.
If you want enough raspberries to make jam or something, start with 4 or 5 plants. You will probably not get enough the first or second year. By year three, you will have a large number of canes and a prolific harvest. My grandma will freeze them as they come on until she has enough to make what she wants.
Blackberries also spread but not like raspberries. I planted two plants of a thornless variety. I get huge, huge berries. You have to pick them when they are just right or they are super sour.
In the photo below, the ones that are not dark black almost killed me.
There is much information online regarding berries and how to prune and grow them. If you want a good crop, you have to prune them.
Check this pruning guide for more information.