Here is what you need to do.

- Find the image you want and download it.
- Go to the Mecabricks Parts Editor (access it by clicking on the 'PARTS' button on the header here)⬆and find the piece that you want to have the logo on. It will probably be in something like 'Flat Tiles' or 'Bricks'.
- Click on it. If the dialog in the right-hand side of the screen has a 3D version of the piece that you can move around has a button below it that says 'EDIT', that means that it has been converted to the relatively new parts system and that you can make a custom decorated part from it. If it says '3D data not available', you're out of luck.
-Once you find a piece that works, look at the number in the grey box right below its icon. That is the piece's Reference. It is also its Configuration. For undecorated pieces such as these, the reference and configuration is the same. However, for decorated pieces, the reference refers to the printed piece, but the configuration is that of the mold from which the the printed piece was made. This will be important later. 
-Now that you have the piece's configuration, switch over from Official to Custom in the dialog on the left-hand side of the screen. In the box labeled 'CONFIGURATION', type the configuration of the piece you want and hit Enter. 
-In the Materials box, click on the white circle with the line through it. Choose the color you want your piece to be. 
-In the Decorations box, switch from 'Plain' to 'Decorated'. A 'TEXTURES' dialog will appear on the right-hand side below the 3D View. Right under 'UV LAYOUTS' will be the uv maps for the piece. For something like a tile or a brick there will probably only be one. Next to the name of the uv map will be a Download button. Click on it.
-In the image editor of your choice (if you don't know your choices, Inkscape and GIMP work fine and they're free), open your uv map. Import your logo as a new layer on top of it. Use the fill tool to change the background color to transparent (the white and grey checker color). If you do not do this, the background will be part of the texture and you will not be able to change the color of your piece. 
-Resize and move the logo so it is where you want it on the uv map. The uv map is, put simply, all the sides of the piece unwrapped and laid out flat. Wherever your design is on the uv map will correspond to where it is on the piece. 
-MAKE SURE THE VISIBILITY OF THE LAYER WITH THE UV MAP IS DISABLED and export the texture, giving it a meaningful name like 'OEC logo color texture'.
-Go back to the Parts Editor and click on the + button next to the Color box of the Decorations section. Select the logo texture that you exported. The texture will appear on the piece in the 3D view.
-Now you fill in the piece's reference and name. The name is generally much longer and more descriptive than the reference. You can put literally anything you want in there, but keep in mind the reference will appear below the piece's icon in the workshop, and it should be fairly concise, memorable, and easy to type.
-Hit CREATE. 

Good luck,
Corvinus

Idk why but it doesnt let me do the stuff i see the others do everything is blank and i cant select anything

Chances are that you are still in the 'Official tab'. Make sure you are in the 'Custom' tab. If this is not the case, could you post a screenshot?

Could i post a screen shot of what the logo?

No, I mean a screenshot of your computer screen where you can see your problem.

It's not letting me press on the circle with the line through it...
I'm confused!

And where is the decorations box?

Try this (it has pictures):
HOW TO MAKE A CUSTOM DECORATION

I have a problem, and the problem is that it won't let me select the tab that says Custom, what do I do?