Some of the markings on it.
Between the bolt and the sights it is marked "CR 868"
The band by the stock says "ER Enfield 1905 SHTLE T***"
SHTLE=Short Magazine Lee Enfield or SMLE
Yours is a MKI*** model.
Is this a gun case gun or something that is useable?
Absolutely usable
If its a good gun to use can I mount a scope to it?
Some of the SMLEs such as the no1MKII and No4 series rifles have clamp on scope mounts, but I'm not sure about the MKI rifles. If it needs to be drilled and tapped, the cost of mounting the scope will be far more than than the price of the gunsmithing, scope and mount combined- the rifle is worth a lot of money if it hasn't been tampered with- drilling and tapping the receiver will knock $500-1000 off the value of your rifle.
What are the things on the left hand side... they almost look like another pair of sights?
A volley sight- Brittish soldiers would amass fire upon a distant target firing in formation using the volley sights- sort of the same effect as a machinegun before machine guns were common.