This forum is generally a English speaking forum.
Firstly when asking for help, without knowing the contents of the error message we sometime cannot help.
Anyway from looking at your image I would suggest you have a look at the dynamo primer(About | The Dynamo Primer) and maybe have a look at the example scripts(Example Files | The Dynamo Primer) because it is best that you have a look at all the fundamentals on how things need to be done then you can expand from there. The cause of your issue is that you are using a node that will output the start point of a curve(eg a line, arch,etc) that you would input.
For a straight line you need a start and a end point to be able to create it.
Was just preparing a example and you beat me to it 
Hopefully the attached script will give you a good learning example script, it is a very old learning script i created when i was just starting out with dynamo in 2014.
I just just opened it in Dynamo V3 for the image and save as to upload here, it does not require any packages.
Bridge.dyn (45.9 KB)
thanks you very much
thank you very much. please my code block doesn’t give the same result as yours.
@bmsoinfo35 it looks like you’ve got some copy/paste errors in those code blocks. Instead of pasting each line at once, start a new code block and paste them line by line until you get the error, then address the lines one at a time.
It appears you’re just getting started on your journey with Dynamo, so I recommend you go though the Dynamo primer in it’s entirety - skip nothing as each exercise is designed to teach you a topic not produce an outcome. https://primer2.dynamobim.org/