If you just butter or grease your cake mould, the cake mixture won’t have anything to grip onto to help it rise (it will slide and shout ‘help’ as it goes down). Flouring the mould after you grease it will help the cake to rise nicely. Your options include:
OPTION 1 (especially if you want a clean cake with no traces of greaseproof paper marks):
Use a small piece of greaseproof paper to spread a thin layer of butter inside the whole cake mould. Get a few tablespoons of flour and shake it around the bottom to coat it in a thin layer of flour, then turn the tin sideways, and turn the tin while tapping to also cover the sides in a thin layer of flour.
OPTION 2 (I use this one for tins with removable bottom circles – you need the paper because otherwise there are ridges the cake can stick to): use a small piece of greaseproof paper to spread a thin layer of butter inside the whole cake mould. Cut a circle of greaseproof paper and put it at the bottom (be careful not to touch the buttered sides of the cake tin) then tip the cake tin sideways, get a few tablespoons of flour and turn the tin while tapping, to cover the sides in a thin layer of flour.
If I see a fingerprint where the flour isn’t sticking, I might try to butter and flour that little bit again. It is sometimes necessary to clean the whole thing and start again.
Sometimes you’ll see little lumps of flour. If they are big lumps then clean the tin and start again. If they are very little then don’t worry – it will probably be fine!