Follow it through.
Starts with a loop. It'll only run once. It creates an integer (i) with a value of one, then sets the loop condition to check if i is greater than or equal to one, and to increase the value after the loop runs (i++).
Then it just runs through a bunch of variables.
First, it sets variable y to the value of i as a string (type casting), so y = "1"
Then it sets variable x to "C:\\", the first backslash escapes the second so it actually assigns the value correctly. It'd probably error when running without it.
Next it creates two strings, z and yk, with some random text. It's not important what the values of these strings are.
It then creates a variable sc that contains the values of z + yk, so sc now becomes both of those two random strings of text in the previous two lines.
Next it creates variable gh and assigns it the value of x and y, so gh = "c:\\1"
Next line creates variable lp, assigns it gh+".txt", so lp = "c:\\1.txt"
Now it creates the actual file (c:\1.txt) on your hard disk.
Next line opens that file so that the following line can write data to it.
The line after that (bn.write(sc)) will write the data in the sc variable (the two random strings that were concatenated)
Then it closes the writer stream and tells you it's done.
When it's done, you should be able to open c:\1.txt and see the data written to the file.