Step 1. open freeways.
Step 2. press Ctrl + E.

Once you've entered map editor, you'll see this.
https://images.steamusercontent.com/ugc/12021109373863391704/772B7ADD55A40478D24DC2A8113F6187726BDEC9/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

Then, click one of the 81 rectangles.

Now we're gonna add some buildings or roads.
If you moved your cursor to the edge of the board, It'll be Roads.
If not, It'll be buildings instead.
https://images.steamusercontent.com/ugc/16889656377470802086/97DC667E04F2F319ED64E5E20AE5D57834DC1B47/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

You can change the road number by clicking the road and pressing <, >
You can also change 'east' or 'north' into something else by clicking the road and pressing M.
You can change colors by clicking the road/building and pressing C.
If you click the building and press A,S You can change the building skin.
If you click the building and press I,O You can change the building Entrance and Exit.
If you shift click the building and drag it, You can Change the size.
Add some more buildings and roads.(I only added roads.)

If you misplaced it, Click the road/building and press Delete.

https://images.steamusercontent.com/ugc/10955464983810674881/46875E689B73EAEC4524CBF422E4DE6368CFA12A/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

Now, we're gonna add some obstacles.
Add obstacles by pressing W.
If you click the Obstacle and press A,S You can change the Obstacle.
If you shift click the Obstacle and drag it, You can Change the size.
If you click the Obstacle and press C, It becomes A building.

If you misplaced it, Click the obstacle and press Delete.

https://images.steamusercontent.com/ugc/17110896312441109665/FE9AC89E31CFF46341035320413A53D3049EDDA0/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

Now we'll decide how much traffic wants to go where.

Click a road/building and put your mouse on an another road/building and decide with -, = buttons.

https://images.steamusercontent.com/ugc/13161695315268275726/B7C9B7904F1CFD52AB958CD1C486941221334E06/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

Now it's done. Press ESC to save.

Press E and play!

If you wanna edit again Press E again.
If you wanna exit into normal mode press Ctrl + E.
https://images.steamusercontent.com/ugc/10297940403140245305/34BFEFD450E403B13624ABFA5EE1DB3C83A56EF4/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false