For the following example we assume the following:
9A1hB7KnXrrU6SHXmneiuMPMDugkteYJTBz35reKeiUMYsrlIIOYznZuU7Z6eAoQSKWINaG5hDP0Dxp4rSnhRDNiA1ErshZxiBdfoEOV5YGf9k1F/ws/stock (to get all articles the user has on MKM)The most important thing to take care of is the OAuth Header. That's why you find everything about it there. Once you're familiar with building the OAuth header, it's easy to request protected resources.
GET https://api.cardmarket.com/ws/stock
Authorization: OAuth
realm="https://api.cardmarket.com/ws/v1.1/stock",
oauth_version="1.0",
oauth_timestamp="1394701063",
oauth_nonce="YPSM0TqkRKSwxOINSiVh",
oauth_consumer_key="9A1hB7KnXrrU6SHX",
oauth_token="IIOYznZuU7Z6eAoQSKWINaG5hDP0Dxp4",
oauth_signature_method="HMAC-SHA1",
oauth_signature="tj1A12h5T2w8QGMjQEF+AUzaMc0="