.op is a single point DC analysis to calculate steady state response of a circuit, it is useful for non-switching circuit.
.dc is to allow sweep of voltage and current source to perform multiple .op opertion to give you the result.
.dc is equivalent to use a .step to change source voltage or current in .op
in electronic, for steady state or DC operation point or bias point, it calculate result of steady state, i.e. time to infinite. But the calculation never require time information as in steady state, because capacitors are fully charged act as open and inductors as short circuit. Based on that, calculation can elminate all time dependent elements and perform calculation. You normally learn this technique in circuit theory especially in calculating transistor bias condition. This technique is useful to get steady state result except for circuit with switching elements (e.g. switch, logic or dll block). For switching circuit, it normally require transient analysis to get result at steady state.
In short, .op .dc or .ac has no time information. In electronic, we learn how to solve circuit without going into solving differential equation, which means eliminating time in the formula.
In transient analysis, .op is performed before transient is run. This represent .tran firstly assume circuit is reached steady state and to start calculation. In real life, for example, you normally run power for audio amplifier to allow its reach steady state before apply audio signal. So, steady state result became t=0 starting condition. If you don’t want .op before .tran, you have option by adding UIC in .tran.
.op, .dc, .ac and .tran are four basic directive in any spice simulator and not unique to Qspice. You should able to get detail information from internet or textbook.