The Mini-Roman 2D opening is similar to the Roman 2D opening. Both show a 3-suited hand with some singleton or void.
The Roman 2D is based on 17+ HCPs, while the Mini-Roman 2D shows 11-15. Both point ranges can vary somewhat per partnership agreement.
Responder has a very accurate description of opener's hand, other than not knowing the precise location of the short suit, so responder is normally in charge of the bidding.
Without enough combined points for game, responder can bid his lowest suit. If opener is not short in that suit, he passes; otherwise, he bids the next suit up the line. Responder can then pass with a fit, or he can place the bid in a different suit, knowing that opener will have at least 4-card support.
With more points, responder first bids 2N, which asks opener to bid his short suit. Knowing opener's HCP range plus his distribution, responder can usually place the contract when there is a fit:
If you bid 2N intending to invite with a 5-3-3-2, you may be forced to bid 3N if partner is short in your suit, so you should have two stoppers in your suit and be at the top of your inviting range.
With a second suit, such as a 5-4-2-2 or 5-4-2-1 hand, you can fall back to your second suit to invite, so you can invite with a point or two less and/or without good stoppers in the long suit.
If responder's RHO bids, responder is no longer forced to bid, but may still bid 2N to ask for opener's shortness. A double is penalty-oriented; opener should pull the double if short in intervenor's suit.
Some people play that opener rebids the suit below his short suit to give responder room to ask for more information.