Enduring actions and state with ている and てある

Let’s look at ている and てある now. They make use of いる/ある as auxiliary verbs.

ている indicates an enduring action or state. For a lot of verbs, this means progressive or continuous (enduring action), but for others, it means the result of an action remains in a certain condition (enduring state).

食べている 
I'm eating. (enduring action)

死んでいる
He's dead. (enduring state)

The い in ている is commonly dropped in conversation, both in writing and in speech. This includes ます form to (as てます).

食べてる
I'm eating.

ておる is a formal variant of ている. おる and いる have mostly the same meaning. ておる can be spoken as とる.

何を言っておるのだ。
What are you saying

てある is about something being in an enduring state resulting from someone’s action. てある always expresses a resulting state, never an action.

晩ご飯はもう作ってある
Dinner has already been made

てある can turn the direct object and into a subject. This means that the verb's normal "logical object" gets marked by が or は (or unmarked), like dinner in the example above. However, because Japanese is linguistically weird, sometimes を can be used, too.

Finally, it expresses a state, not an action, so てある should not be considered "the passive" version of the verb. Japanese has a real passive that we'll cover soon.