Hi Joseph,
in general you can do it in two different ways.
1st – very easy and recommended:
It’s almost the same like in Minecraft. While holding SHIFT you can move to any edge and won’t fall down. Doing this grants you sight of the “front side” of the block.
Then you can set another block behind this block “into the air”.
I recommend to do this about 3-5 times and then build the other parts along from the small “path” you have buildt into the air.
2nd – the “if nothing works” method:
You can jump down that bridge and get yourself up with dirt again 🙂
Well ok this isn’t really a way how it should be done but can be useful sometimes though.
If you have any other question feel free to ask it 🙂
Greetings
Bojeya!