Filenames that begin with a dot (or period) are hidden files on Unix-like operating systems. That means dot files are usually not listed when you type the
ls command at a shell prompt. Type
ls -a to see all files in a directory, including the hidden ones.
A common dot files is .htaccess to store web server configuration settings for a directory.
When you type
ls -a you'll almost always see two directories named '.' (one dot) and '..' (two dots). They are not directories in the regular sense, but represent the current directory and parent directory, respectively. For example,
cd .. will change your present working directory to the parent directory.