I do not use LAML with DrScheme, because it is slow and relatively inconvenient. For novices, however, DrScheme may be a good choice because it is very helpful and pedagogical. Here is how you do it.
First choose language level using the menu point 'language>choose language...'. Set the language level to PLT textual (includes R5RS).
Then follow the general advice on how to use LAML from a Scheme interpreter. Issue the commands in the Interactions window of DrScheme. This procedure allows you to use the laml procedure and the other high level LAML commands
In case you want to process an existing laml file (a file with 'laml' extension) by simply executing it from DrScheme, the first few lines of the file must be modified slightly. Usually, the start of a LAML file goes like this:
(load (string-append laml-dir "laml.scm")) (laml-style "simple-html4.01-transitional-validating") ...
Now, replace this prefix part with something similar to
(define laml-dir "c:/laml/") (load (string-append laml-dir "laml.scm")) (fake-startup-parameters "index" "c:/laml/") (laml-style "simple-html4.01-transitional-validating") ...
It is quite tedious to write these slightly redundant informations in each and every LAML file. The other modes of LAML activation take care of these details for you. But this cannot easily be arranged for in DrScheme.
In line 3, use the actual source file name (without extension) as first parameter and the working directory (the so-called LAML startup directory) - full path - as the second parameter. Notice that the startup directory can be different from laml-dir, as defined in the first line. Remember to terminate all directories with a forward slash, and never use backward slashes in directory paths.