What kind of template?
If it is jsp, you can just place it anywhere you want in that folder and reference it from the template definition.
If it is freemarker template, those are by default served from either the classpath or from repository, so for testing you can just upload it to the repo via templates app http://yourtomcat:port/magnoliaAuthor/.magnolia/admincentral#app:templatesApp:;
BTW if you install samples module (add magnolia-templating-samples.jar in your WEB-INF folder), it will create folder "templates" in your webapp and extract sample jsp templates in that folder.
HTH, Jan