Nuisance email

Questions:

I am getting a lot of unsolicited e-mails, is there anything I can do to stop them?
I have been surfing the net and have come across a web site that is condoning and encouraging violence against homosexuals/ muslims/ catholics/ jews/ women/ animals/ doctors etc? What should I do?
My friend/ex partner/ex employee is sending me threatening/nuisance e-mails/texts/phone calls, what can I do?

My ex partner has got access rights over our child but my son/daughter has to be back by 1600hrs and he/she has not brought my son/daughter back yet, what can I do?

For police non-emergencies dial 101