It depends in what voice it's written in. In a lot of Bach for instence... I'll just make up an example. Say theres a whole note "C" on the staff top voice... And it's TIED to the next measure quarter note C, but there is a lower voice with many other notes going on. You want to hold the C with one finger and play all the other notes with all the rest or whatever...
A slur is different... You can tell if it's the same voice... If like allchopin said an F then a lot of notes then another F, if it's the same note it's a slur still. IF it's the same voice. It's pretty obvious 99% of the time... But it doesn't have to end in the same note to be a slur. At the end of a slur, which is usually a phrase, you "lift". Make the last note a little "shorter" not quite SHORTER but just have a little tiny maybe rest in between that note and the next slur or note or WHATEVER... It's an audible lift and is very important phrasing technique.
In a wind instrument it means to not tongue the notes within the slur. And then when the slur ends you tongue the next note which gives pretty much the same impression of the lift. Everything under the slur with piano is played legato and then the lift at the end like I said.
Hope that's what you needed I'm not quite sure I made a lot of sense! I have problems with that sometimes
