This is for England. Not for Scotland or NI. I don’t know about Wales
The forms are downloadable from the link @Autumcolors gave, along with guidance notes which are very helpful, telling you the implications of your choices and what you might not be able to do if you make this choice. Try downloading the paper form and filling it in just as a practice, reading the guidance notes as you go.
Basically, it’s simple. You choose up to 4 attorneys who can act for you, in your best interests but according to your wishes, if you lose your marbles. And one or more replacement attorneys. So you could appoint DH and DC1, with DC2 as a replacement in case DH goes before you.
Then you decide whether they act jointly - they all have to get together and sign for everything however trivial - or jointly and severally, in which case if one of them is buying toothpaste for you, they don’t have to get the other’s agreement.
The PoA for Health can be used only when you’ve lost capacity. You can decided whether the Finance one is the same or whether it can be used earlier - useful if you still can manage things but are fed up with the paperwork.
Once you decided on this and filled in the forms (and the guidance tells you precisely what order things can be signed in and who can witness), you submit it all to the OPG, and once it’s been returned and stamped by them, it’s ready for use when needed.