Let us look at how to think about the concept of Forcing and Non-Forcing bids by looking at practical auction:
You hold the following cards in the East position.
♠KQJ6
♥AQ6
♦K5
♣J643
The auction begins with your partner Opening 1C:
W N E S
1C
Is the 1C a forcing bid?
1C is a non-forcing bid. Responder is allowed to pass as the opener is limited to a range of about 11-21 HCP.
The auction continues:
W N E S
1C P 1S
Is the 1S bid forcing?
1S is a forcing bid. This bid is forcing because the bid is unlimited.
The auction continues:
W N E S
1C P 1S P
1NT
Is the 1NT bid forcing?
1NT is a non-forcing bid. The opener is showing a limited hand with 12-14 HCPs. A responder without a strong enough hand to invite to game opposite a 14 HCP balanced hand is allowed to pass.
The auction continues:
W N E S
1C P 1S P
1NT P ?
Responder has 16HCP. Opposite a 12-14 HCP hand, responder knows that the partnership belongs in a game contract. This means that the responder must choose a bid that is forcing (or a game contract) and must avoid making a (non-game) rebid that is non-forcing.
For example the east player must discard the choices of bidding 2C or 2NT because these bids are non-forcing.