This is general information, not legal advice. For anything valuable, talk to a qualified IP attorney. The Intellectual Property Office (IPO) on GOV.UK has official guidance.
Copyright — automatic
In the UK, copyright applies automatically to original written, artistic, musical and photographic work. You do not register it. Keep dated drafts and source files — they help show the work is yours.
Designs — the look of a product
The shape and appearance of a product can be protected. Some protection is automatic (unregistered design right), but it is limited; registering a design with the IPO gives stronger protection and is relatively inexpensive.
Trade marks — names and logos
A registered trade mark protects your brand name or logo for specific goods and services. Search the register before you fall in love with a name.
Patents — how something works
Patents protect new inventions — how a thing works or is made. The invention must not be made public before you apply, so keep it confidential until you have advice.
NDAs
A non-disclosure agreement is useful when you share an unprotected idea with a manufacturer or partner. It will not stop a determined copier, but it shows the information was shared in confidence.