Use CAST  or  CONVERT  

select convert (varbinary (20) , "select") it gives = 0x73656c656374
then you can convert that to a varchar
select convert (varchar (20), 0x73656c656374 ) it gives "select"

Use master.dbo.fn_varbintohexsubstring(1,@binvalue,1,0)

master.dbo.fn_varbintohexsubstring(1,@binvalue,1,0)

declare @binvalue varbinary(256),
@vcharvalue nvarchar(256)
set @binvalue = 0xF5FF3FED3B055DF7EC27251FBC80EE48
select @vcharvalue = 'aa' + master.dbo.fn_varbintohexsubstring(1,@binvalue,1,0)

print @vcharvalue

it gives = 0xF5FF3FED3B055DF7EC27251FBC80EE48

Use master.dbo.fn_varbintohexstr(@binvalue)

declare @binvalue varbinary(256),
@vcharvalue nvarchar(256)
set @binvalue = 0xF5FF3FED3B055DF7EC27251FBC80EE48
select @vcharvalue = 'aa' + master.dbo.fn_varbintohexstr(@binvalue)

print @vcharvalue

it gives = 0xF5FF3FED3B055DF7EC27251FBC80EE48