Gill what you are asking about is basically called field craft,it's a wide ranging subject and probably worth digging for. how it is applied would depend much on the subject you want to find and shoot plus what you want to do This is your fun,to some extent what works for you or what you enjoy doing is the best way . Two togs can approach a subject in different ways one isn't right the other wrong.
Field craft essentially means learning about a bird or animal and applying that knowledge to get close to me. It's almost a separate thing to learn to the side of actually using and learning how to use the camera. you can walk up to some subjects, or sit and wait it is your choice,but obviously knowing about your subject's habits will mean you will have a better chance of choosing the right one for you in a given situation at a given time. Gill you can find bird hides at reserves WWT local wildlife trusts etc which might present yo with chances. You can use a pop up hide you can cover yourself in camo, you might not need either but without subject knowledge even if you apply both you might never see the subject you want to see because you don't know where it lives what time of day it might present a chance etc,
Gill it's such a wide ranging subject to cover it here is tricky it's a skillset basically hard won by each individual and also tailored to what that guy /gal has fun making images of. I suppose sitting and waiting and for how long is almost a piece of string question,some of us spend hours days weeks even trying to get an image maybe a certain image. Those hours spent and degrees of frustration are part of this game,but the subject knowledge field craft will mean the tog is at least waiting in the right place with a goodly guess of when the subject might show up,luck is a player wildlife birds do what they want to do.
Gill Have a dig on fieldcraft and wildlife or bird photography find what appeals to you,you having fun is important in all this . you can make a hide at home feeders etc reflection ponds are fun, or travel the globe,there are hotspots togs often go to already mentioned in a reply above both in blighty and across the planet. You might never want to see another sole just be out in a wildplace waiting for a humble wabbit,tis your photography. You can even pay for someone else to do the craft say pay for a hide to shoot kingfishers,it's all your choice.
Some specifics regarding getting closer, move slow don't stare at a subject all the camo in the world won't help if your movement is erratic, don't necessarily take a direct line in your approach use cover if necessary,don't really know what else to write mate without making this an essay,so have tried to give some pointers for you to research off.
Oh I'm a novice tog who bumbles about in head to toe camo as a rule,i'm not terribly fond of hides but have no probs using them,I just like being free to move really.
Have fun Gill,one last thing,field craft..... knowing your subject,has another side I just thought I'd mention,it's the bird or beasties well fare. If you know them you will have a good handle on what you might do to disturb or stress them,This is desparately important knowing when to back away or leave alone is good knowledge to have. Some subjects might have legal resrtictions placed on say photographing them breeding,for example again worthy of mention.
take care
stu