NOTICE: GIMP IS NOT AVAILABLE FOR MOBILE!
@ollywhxte suggested a GIMP tutorial, so I'm putting one up for you guys. There's a more popular way to do this, but I find this to be easier to do.
I'd like to remind you all to take your time with these liveries. Patience is probably the greatest part of making a livery good, so don't make one all in one sitting. The livery here is only an example, to show you the twists and turns of making liveries, and isn't really that good compared to what I or everyone else on AE puts out.
Firstly, you need GIMP actually installed. It's available on Mac, PC, and Linux, so it'll be accessible for most of you. You won't have a hard time finding the site to install on Google, but if you need the link, click here.
I'm assuming you've downloaded GIMP already. Okay? Good.
You'll need a template, and you can get them We have all kinds of planes available from Med as well as others who have volunteered to make some.
Okay. You're in GIMP, and you have a template ready for use. For reference, I'm using an A320, but use whatever you'd like. This process is standardized so it works on whatever template you want.
Now, I usually get started with the tail first before moving on to the fuselage and engines. Bring whatever elements or pictures you want to incorporate into your livery into GIMP to keep organized.
Alright, now let's get into the nitty gritty. Working on the tail first, click on the TAIL layer, use the Fuzzy Select tool (the magic wand), and click on the physical tail. If you don't do this, then all the drawings and photos and stuff you put in will "spill out".
I'm going for a simple livery this time, so get out your colours and use the Bucket Fill (the spilling bucket) to apply a solid layer of color.
Now that that's done, you'd want some decals to spice up your plane. Simply go into the menu of the picture you want, go into the Layers tab, and drag the picture into the livery.
If you did it correctly, the decal should appear like so:
But you want to actually put the decal on the tail, correct? No problem. Go into the Fuzzy Select menu by clicking the Tool Options tab, and click the 3rd selection (the one with the grey outline, shown below).
Then, go to the TAIL layer and click on the selection to remove it. You did it correctly if the outlines disappear.
Now, go into the decal's layer (which ends with copy) and use the Scale tool (a small rectangle on the top left corner of a larger one) to resize it to whatever fits best on the tail.
Next, just use the Move tool (4 arrows going away from a point) to move it into the tail (NOTE: IF YOU HAVEN'T PLACED THE DECAL LAYER BETWEEN THE TAIL AND TAIL DETAILS LAYERS, THEN DO SO NOW).
You now want to move on to the winglets and engines. Those are really easy. Simply click use the Fuzzy Select again and revert it back to the first option, click on the appropriate layer, go into the Bucket Fill, and click inside the outlines with it.
Now let's get into the fun stuff; the fuselage.
By now, I'm sure you know how to deselect Fuzzy Select outlines, so do that.
Select the FUSELAGE layer with the Fuzzy Select, and just do as you please. I'd like to fill the lower portion with red, however. Grab the Paintbrush tool (you can guess what it looks like), place the brush at the end of where you'd like to paint, click, hold Shift, and drag it to the other end. Click when you're happy with the line you've made.
Now grab the Bucket Fill and click on the portion below the line.
Now it's time for the name. Have your airline name on hand and click on the Text tool (an uppercase A). Write the name, highlight it, and change the font from the default Sans to something else, or resize it. This is the time where I suggest you download custom fonts for your computer. Just Google "free fonts" and sites like dafont.com, fontspace.com, fontsquirrel.com, and urbanfonts.com should show up.
You have almost everything done, except the registration. I've gone over everything you need to do for this already. Drag in the flag(s), resize, move them with the Move tool, put in the actual code (download the Amarillo USAF font for this, it works great).
And you're done! Feel free to add additional details, replace colours, or maybe even add a background.
Come back in some time, tinker around, and you might end up with something better.