Ok - Now I can see what you are talking about.
In m. 12-13, (not 13 - 14) the Bb quarter note is tied to the first eighth note because it is being held for 1 1/2 beats = the same as 3 eighth notes tied together. If this were in the middle of the measure you would have a dotted quarter note. However, because it continues into another measure, it has to be done through a tie. (I can use the word "beat" here because here the quarter note is actually a beat because it's in 4/4 time - re: the other conversation).
The same symbol is also a phrase mark or a slur. When different notes are covered by this mark, then it means all of it is one phrase, that you might sing in a single breath. It forms a musical unit. Play it and see if you can feel that unit. When the phrase mark goes upward, downward, or horizontally it simply is following the direction of the note heads, so that the ends of the symbol can be close to them. It makes reading easier.