Labmatrix is a web-based application, and is accessible at the URL https://labmatrix.nci.nih.gov/labmatrix/. Your login credentials are your central NIH username and password.
Manuals for Labmatrix can be found at the bottom of the home page once you've logged in.
Labmatrix Lab Loader
If you are importing clinical labs or cultures, you'll also be using the Labmatrix Lab Loader web application, which lives at https://lmlabs.cancer.gov/; your account information is again the same as your NIH username and password.