An EA's inputs are the settings shown on the Inputs tab of its properties window. They are the parts of the program the developer chose to expose. Some are meant to be changed, such as the risk level. Some are there for convenience and should be left alone. The way to tell them apart is to ask what the developer expects you to know.
Settings that belong to the owner
The risk setting, since it depends on the owner's tolerance for drawdown. The mode, if the EA has modes, such as a prop-firm mode or a lower-drawdown mode. The magic number, which distinguishes this EA's trades from others on the same account. A maximum spread beyond which the EA will not trade, since spreads differ between brokers. A symbol mapping, if the EA trades several markets under names that vary by broker. Switches for optional filters, such as a news filter. All of these are about the owner's circumstances, not about the strategy.
Settings that do not
Indicator periods, multipliers, thresholds, and anything that decides when a trade is taken or where its stop sits. These are the strategy. If they are exposed, the owner is invited to optimise them, and optimising a strategy on recent data is the fastest way to destroy it. A developer who exposes dozens of such parameters has either not decided what the strategy is, or has decided to let the buyer take the blame when it fails.
Why defaults exist
The default values are the settings the strategy was developed, tested and, if there is a live record, recorded with. Changing them means running a different strategy from the one with the evidence. That is sometimes a reasonable choice. It is never a choice to make without knowing it has been made.
An EA has 62 inputs, including the periods of three moving averages, an ATR multiplier for the stop, an ADX threshold, and a "profit factor filter". A buyer runs the platform's optimiser over the last two years and finds settings that double the backtested return. Live, those settings lose money in the first quarter, because they were fitted to a period that has ended. A second buyer leaves the defaults and gets, roughly, the record the vendor showed. The first buyer blames the EA.
Save the settings as a .set file before changing anything, so that the defaults can be restored exactly. Change only the inputs the documentation describes as the owner's, and note the date of every change beside the trade history, since a change in settings is a change in strategy and the record after it is not comparable with the record before.
When choosing an EA, prefer one with few inputs, all of them explained, over one with many. A short list of owner settings and a compiled, fixed strategy is the design of a developer who has finished the work.