Sessions are the way Flask will store information across requests; to do this, Flask will use signed cookies using the previously set SECRET_KEY config to apply the HMAC-SHA1 default cryptographic method. So, a user can read their session cookie but can't modify it. Flask also sets a default session lifetime that defaults to 31 days to prevent relay attacks; this can be changed by using the configuration key's PERMANENT_SESSION_LIFETIME config key.
Security is paramount in today's modern web applications; read Flask's documentation carefully, where various attacks methods are covered: http://flask.pocoo.org/docs/security/.
A Flask session object is a special kind of Python dictionary, but you can use it much like a plain Python dictionary, as follows:
from flask import session
...
session['page_loads'] = session.get('page_loads...
