These expressions are common in classical guitar music.
ten: means tenuto, which is a playing style used for effect. Each note should be held for its full length. Do not confuse this with legato, tenuto is holding notes for their full length but not necessarily playing them smoothly or softly.
C.2a Is a barre. This is unique to stringed instruments and it is when you lay one finger (usually the first finger) across all or some of the strings on one fret. A full barre is across all six strings, while a half barre is across the top three or so strings (sometimes four). The number shows you which fret this is done on. the
------¬ written after this shows you how long to hold the barre for in the music, and you should lift your finger at the end of the line.
I have not seen a barre written in this form before, usually it is written as a capital 'C' followed by roman numerals for the fret and the same line indication. A half fraction before the 'C' (or a dash vertically through it) indicates a half barre: