Music Notation -Note relationships Playing Ties/ Slurs

[charleyjunior]

As I continue to develop my  piano sight reading skills, and after listening to many you tube performances there are inconsistencies in how to play. Two pieces are being reviewed:
Rachmaninoff's Prelude Op. 32, No 10 and Ravel's Le Gibet.  Please give a clarification that
meets with the definitions in standard Music notation dictionaries defining Ties and Slurs.

[scottmcc]

ummm....a tied note takes the value of both notes combined, a slur indicates phrasing.

now, which specific parts of those two very challenging works are confusing you?  measure numbers would help.