i have set up email addresses for two of my colleagues but have no idea how they can now access/use these accounts!! im a bit inept at this whole thing - help please?!

I have added dan@caspabromley.org.uk and sarah@caspabromley.org.uk as email addresses I'd like to allocate to two colleagues. I have no idea how they can now access and use these accounts....... please help me! i will also need to add further addresses in the future.