The slur and tie look very similar. The difference is that a tie connects two notes that are the same and the slur connects two notes that are different pitches. In both cases you do not rearticulate the second and following notes.
The slur has some very specific meanings for certain instruments such as the orchestral strings where it is used to mark notes played with one bow direction or guitar where it symbolizes pulling off or hammering down on the fretboard. In all cases the sound is similar in that the second and following notes do not have as strong of an articulation as a regular note.