Fumer is a french first group verb. So it follow the regular conjugation pattern of the first group like: 
aimer.
										Follow this link to see all the endings of the conjugation of the first group verbs : 
conjugation rules and endings for the first group verbs.
																																						
																												Fumer is conjugated the same way that verbs that end in : 
-er.
																												First group verbs always end with 
-er as their infinitive. Endings of first group verbs are regular.
Note : Although endings are perfectly regular, spelling changes occur in the stems of verbs in 
-cer, 
-ger, 
-yer, 
-eter, 
-eler, 
-é-consonne(s)-er, 
-e-consonne-er, verb 
envoyer and similar verbs.