Submitting planning applications in the United Kingdom is a process that has become quite streamlined in recent years, thanks to the release of the Planning Portal, an online service that will determine what you need to do to submit an application to your local planning authority, and that will then collect those documents, and forward them for you, as well as tell you what fees are required for the application to be considered.
The forms for applying for planning permission are quite detailed, and you may sometimes feel like they are asking for too much information, or information that is not relevant, depending on what it is you are applying to do. This is because the basic form is used for everything from change of use to building a home extension, or making massive changes to the structure of a building. There are supplemental forms required for major changes, but the basic form is used to get an idea of exactly what is going on - which is why you will be asked for a bill of materials, even if all you want to do is change a shop into a garage.
If anything is not applicable to your circumstances, all you need to do is note that on the form and make sure that you clearly explain exactly what it is that you are planning to do.
After you submit the application which includes a planning application map, people in the local area will be informed about your plans, and given a chance to object. There is a notice period for this, and you will not be able to do anything while you are waiting for the notice period to end. In general, unless you want to do something like open a night club on a quiet residential street, it is unlikely that you will be told that you cannot go ahead because neighbours have objected, but this formality must still be observed.
If there are no objections from local people, then there will be a consideration by the planning committee. The committee has other criteria that they use to decide whether they want to approve applications - including making sure that the application is safe, that the building will not be an eyesore, that the local roads and transport links will not be affected, and that the building project or the intended use of the building will not negatively impact on the local area's economy.
Assuming all of this is OK, you will be granted permission to undertake the project. If you are refused permission, then it is possible to appeal, although this can be a difficult process depending on why you have been refused planning permission. You may want to seek legal advice to ensure that your appeal gets the appropriate consideration. To ensure that your application gets the best possible consideration in the first phase, make sure that you supply everything that is asked for - including accurate Ordnance Survey maps and any supplementary forms that are requested. Proofreading and double checking your application before you submit could save you not only money, but also disappointment.