You said "free," but you also mentioned "nothing expensive like Photoshop"; there are solutions to your problem that do cost something but are nowhere nearly as expensive as Photoshop.
Pixelmator is great for certain kinds of quick image editing. It's only $30 right now, though that will probably go up when the next major release finally comes out; I believe it's normally $60.
There's also Acorn, which is very similar and perhaps a hair's breadth easier to use, though since they've already had their first post-App Store major version release, it's more expensive at the moment ($50).
If it absolutely must be freeware, do have a look at Seashore, mentioned in a comment by Ian C.
You can use Automator.
Open Automator.
Choose Application from the templates.
Add a Ask for Text action. Tick 'Require an Answer'
Add a Create Banner Image from Text action.
Tick 'Use text input as image filename'.
Open the actions options options.
Tick 'Show this action when workflow runs'
Add a Lopp Action.
Control + click on the Loop Actions Title bar and select 'ignore input'
From the Loop Actions's drop down menus, select 'Ask to Continue' and Use the 'current results as input'
Save and run.
You will then be prompted to enter your text.
Then after you ok that you will be prompted to Choose you font.
Use the font size to determine the image size.
example 64 in Helvetica Bold gives me about 46x77
The same font but at size 300 gives me 177x360.
In each case I am only using 1 character.
If you want to do it from 'Selection'
Open Automator.
Choose Services from the templates.
Set the 'Sevices Receives input' to :rich text * and
in* any application
Add a Create Banner Image from Text action.
Tick 'Use text input as image filename'.
Set the Text Style drop down menu to : 'Use Style of Rich Text input'.
Optionally you can add a 'Reveal in Finder' Action
The Size is set by what ever the original fonts are.
To use the Service.
You can select some text, and control click to get a contextual menu. Listed is the services sub menu. Under this you should find your new service that will run on the selected text.
Best Answer
All the software I would normally recommend are probably out of scope considering your comments about Adobe Photoshop, and the fact you're looking for something more user-friendly and simple.
Since you just want to be able to annotate an image and then edit this again later, one option for this type of thing is to use MS PowerPoint (which you already have).
I've shown many people over the years how they can use PowerPoint and most of them have been happy with the results, so give this a go before you dismiss it.
Using MS PowerPoint
One feature of MS PowerPoint 2011 and above is that you can group items on the slide and save them as a single image. So, you could do what you want as follows:
And there you go - you've got yourself an edited (annotated) image you can use that is separate from the original file, and if you save the PowerPoint slide you have a way of going back and editing it again.
PowerPoint also gives you some pro editing features such as the ability to arrange items (e.g. Forwards, Backwards, Front, Back) as well as adding shadows, transparencies, etc. If you take the time to really get to know it, you'd be surprised what you can do.
I hope you don't mind, but I took the liberty of using your profile pic to do a quick edit with it in PowerPoint just to give you a taste of what's possible.