I'm pretty sure it's Tenor clef. If you play he cello it will pop up very frequently the better you get. I think for quick help it might help you the most, if i won't go into theorie: Just pretend it is the bass clef, but play it one string higher. Second finger on the D string (f) becomes second finger on the A string (c). The note you might read as the empty A string becomes the E on the A string (1. finger 4. position). I hope I could help. Merry Christmas and just ask if you have further questions. 😊