Just to get this one out of the way:
Insert card. It should show up in the file manager (and in windows that ask you to select files/folders) automatically. You can just move your documents there from the pre-defined standard folders, create your own folder structure etc. etc.

There's nothing special to it, it works the same way as on your desktop. Plus: It will, of course, free up space on the internal memory which in turn becomes available for installing applications.

I'd very much doubt that you have problems with this approach.

This is, indeed, the more interesting part. Not only will it give you more memory to install applications, it will also speed up things. Internal memory has a compressed file system, like a large ZIP file. While this is good in terms of storage space, the downside is that things become slower (again, like with a ZIP-file that needs to be unZIPped first).

This thread is a more in depth discussion, this one offers an easy, automated solution. The results should be more or less the same.

The only thing I'm not sure of is:
If you don't yet know exactly what you need and why... And if you're not yet a semi-expert on the tablet so you can easily fix things just in case something goes wrong... And if you don't yet run out of space on your internal memory... Will it be worth it?

I'd personally recommend you'd stay with the current setup until you know what's important for you, what you use your tablet for, what eats memory and what doesn't.
It might be that you find out the coolest thing is to have a collection of SD-cards full of video files and pick one or two for each journey... If this is what you'll use your tablet for in the future, cloning to external memory is more or less out of the question (or at least useless) unless you clone to all SD-cards you'll ever use in advance. (Just an example)