Can I record my work in GIMP and post it on YouTube to share my footage with others? for my projects and so forth. Is that legally ok?
Yes it is.
In case of doubt you should definitely ask a lawyer, as an internet forum is not a good place to get legal advice in general. I am not a lawyer and therefore I will not give legal advice. But I have some questions, and their answers may maybe help you finding a personal opinion on which you can base your further activities:
- Is the material you are working with entirely yours in terms of copyright and also in terms of other’s peoples rights? E.g., do you have suitable model releases from the people on photographs?
- Why are you asking? Is it because of the license of the software (gimp)?
- Is the work you want to show by itself legal? E.g., do you want to show how to counterfeit money?
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If this is the concern, FSF position is that program output is not subject to the license of the software itself except for some very specific corner cases which I am fairly certain aren’t applicable to GIMP:
https://www.gnu.org/licenses/gpl-faq.en.html#GPLOutput
But as you point out, there are other possible concerns since the OP’s post was quite vague.
I did that a lot and never got caught. 
You have to look for the rights of your source material (don’t use other peoples images without permission or a suitable license), the image rights of persons or buildings (no Eiffel Tower at night) and of trade marks.