After a 1♠ Opening bid, a Responder with 6-9 points (or 10 pts and 9+ losers) has only two options at his disposal :
      a. raise to 2♠ with 3+card support, or
      b. bid 1NT without it (Responder may not bid a new suit at the 2-level !)

Responder is forced to bid 1NT, even with a singleton or void in ♠s. Responder could also hold 4, 5 or even 6 ♥s with no means to convey this to the Opener.
With a minimum Opening hand (13-15 pts), this is usually not a problem. Opener will either pass, bid 2♠ with a 6-card suit, or bid a new suit at the 2-level when unbalanced.
In this last case Responder will either pass or bid 2♠, showing preference.

However with a strong to maximum hand (16-21 pts) Opener must bid on, for a Game contract in many cases is likely.
In such case Opener's options too are rather limited.
He can rebid :
      a. 3♠ with a 6-card suit
      b. 2NT (16-18) or 3NT (19-21) when balanced
      c. a new 5-card suit at the 3-level

Opener's rebid of a suit at the 2-level will be perceived as a minimum hand (13-15), after which Responder is not obliged to bid again.

The Quijote 2♣ rebid by the Opener (after 1♠ - 1NT → 2♣) shows a strong hand (16-21), is forcing and asks Responder to specify his hand.
Responder's replies can then show a :
      1. minimum (6-7) or maximum hand (8-10)
      2. 4-card or a 5+card ♥ suit
      3. doubleton in Opener's ♠ suit
      4. minor suits distribution when holding 9+ cards in ♣ and ♦ combined

The specific responses are shown below.