--you have to use EXEC or sp_executesql


create table tb (c1 int, c2 int, c3 int, c4 int, c5 int)

declare @var varchar(100)
set @var ='c3,c2,c5'
declare @query varchar(1000)
set @query ='insert into tb (' + @var + ')' + ' values (100,200,203)'
print @query
exec (@query)