Flags are similar to bookmarks. They represent a certain offset in a file. Flags can be grouped in 'flag spaces'. A flag space is something like a namespace for flags. They are used to group flags of similar characteristic or type. Examples for flag spaces: sections, registers, symbols.
To create a flag type:
[0x4A13B8C0]> f flag_name @ offset
You can remove a flag by appending the - character to command. Most of commands accept - as argument-prefix as an indication to delete something.
[0x4A13B8C0]> f- flag_name
To switch between or create new flagspaces use the fs command:
# List flag spaces
[0x4A13B8C0]> fs
00 symbols
01 imports
02 sections
03 strings
04 regs
05 maps
[0x4A13B8C0]> fs symbols ; select only flags in symbols flagspace
[0x4A13B8C0]> f ; list only flags in symbols flagspace
[0x4A13B8C0]> fs * ; select all flagspaces
[0x4A13B8C0]> f myflag ; create a new flag called 'myflag'
[0x4A13B8C0]> f- myflag ; delete the flag called 'myflag'
You can rename flags with fr.