The avocado is the fruit of a tree native to south and central America. It prefers to grow in tropical areas.
Avocados are much higher in fat than other fruits. The avocado has a big seed inside it, and a hard skin, so you can only eat the soft flesh in between. Their flesh is yellow to green, and has a texture that is a little like butter, hence one of their common names of "butter fruit". The flesh of the avocado can be spread on bread or crackers, or the flesh can be diced and used as an ingredient in salads.
Blackberries are the fruit of a very thorny plant closely related to the raspberry. They spread quickly by sending roots under the ground that then sprout new plants. They can easily get unmanageable and are hard to keep under control because of the thorns. Today, you can buy thornless blackberries.
Blackberries are most often used to make jam.
Blackcurrents are a small berry related to redcurrants and gooseberries. They are used mainly for their juice, and made into drinks or cordials. Blackcurrents have a very, very high vitamin C content, with 100 grams of the fruit providing 3 times what you need each day.