Model to perform when given lines (4)
I believe the answer is:
doll
'model' is the definition.
(a doll is a model of a person)
'perform when given lines' is the wordplay.
'perform' becomes 'do' (both can mean complete an action).
'when given' means one lot of letters go next to another.
'lines' becomes 'll' (two abbreviations for line).
'do'+'ll'='DOLL'
'to' is the link.
(Other definitions for doll that I've seen before include "Small replica of a person" , "A girl's plaything" , "Toy representing person" , "Figurine" , "Child's plaything" .)