its pretty easy: first take all berries and put into big pan/pot and add same amount of sugar, so if its 1kilo of berries add 1 kilo of sugar. Leave it for 4-6 hours.
After that cook your pan with max temperature after you see boiling and after that decrease temperature for 5 minute and turn off cooking. And leave it for 10 hours,
And repeat cooking 2-3 times.
After last time wait only 1 hour , not 10 and pour the jam on sterilized jars and cork