You have decided to litigate.
If it is anticipated that a factual dispute will arise during the process, the matter will proceed by way of summons. The parties are then referred to as Plaintiff and Defendant. If a factual dispute is not anticipated, an application supported by affidavits will be made. The relevant document is called a Notice of Motion / Application and the parties are referred to as Applicant and Respondent.
The Plaintiff / Applicant, attacks. The Defendant / Respondent, defends. For convenience we shall refer to the attacker as "Plaintiff" and to the defender as "Defendant".
Plaintiff is well advised to be very sure of it's case before proceeding. Generally speaking in the absence of settlement, there is no turning back. Should Plaintiff at some stage decide to "drop" the matter, it will have to pay the costs incurred by the Defendant up to that point.
Having decided that it has a good defence, Defendant, upon receipt of a summons or notice of motion, lodges a notice of it's intention to defend or oppose. If this is not done in time Plaintiff can get a Judgement. (The consequences are serious). Once done, again, in the absence of settlement, Defendant is locked in, unless of course, Plaintiff withdraws.
Both parties should consider their case very carefully before embarking on litigation.