Notice the syntax in the following example
you have to have a function (ie def reclass) which you pass parameters to (ie a), but in the expression box, you will notice that you pass a field name enclosed in double quotes to the function (ie reclass(!Id!) in the example.
Now the function is specific about indentation. 4 spaces is standard, with the def line unindented. The if statement in my example does an equality check notice the colon at the end. If the equality is met, then the variable 'a' is assigned 1, it is indented 4 spaced. The 'else' section is where program focus moves it a doesn't equal 1, whereby a is assigned 0. Finally a value is returned. Now you can proceed to fix your code. In future, it would be better to copy and paste the snippet, so that people can edit your exact example without having to refer back to an image.
Good luck