Zu dem Fettsack dort hinten in der Ecke sagte ich, dass ...
I said to the fatso in the corner that... 

Weak verbs form the simple past tense by adding -t- to the stem(root) of the verb. You then add the appropriate personal ending: sag -t- e (du sag -t-est ; ihr sag-t-et ).

The past participle is formed by adding ge- and a -t to the infinitive stem(root) -> ge-sag-t.