The MetaTrader 5 page covered the layout and the two switches that let an EA trade. This page covers the features an EA owner meets in the following months.
Indicators and custom indicators
Built-in indicators are added to a chart from the Insert menu. Custom indicators are compiled files with the .ex5 extension, placed in the platform's MQL5, Indicators folder, and they appear in the Navigator once the platform is restarted. Some EAs depend on a custom indicator being installed alongside them, and will log an error and refuse to trade if it is missing. The EA's documentation should say so, and the indicator should come from the same developer.
Templates and profiles
A template saves a chart's appearance and indicators, and can be applied to any new chart. A profile saves a whole set of open charts. Both are worth saving once an EA's charts are set up, so that the layout can be restored after a platform reinstall or a VPS move. Neither contains the EA's settings; those live in the .set file described on the inputs page.
DLL imports
An EA can be written to call external code through a DLL, and the platform asks permission before allowing it. Most EAs do not need it, and a DLL can do anything on the computer it runs on, so the permission should be refused unless the developer has explained exactly why it is needed and is trusted. An EA that requires DLL imports without a stated reason is a reason to stop.
Updating an EA
An update from the MQL5 Market installs through the platform; an update from a developer arrives as a new .ex5 to copy over the old one. In either case: save the current .set file first, note the date, install the update, restart, confirm the EA initialised without errors, and check that its inputs match the saved settings, since updates can reset them. Then treat the record from the update date as a new version of the strategy.
More than one account
A MetaTrader 5 instance connects to one account. To run several accounts, install several instances, each in its own folder, using the portable mode option so their data folders stay separate. The multi-terminal tool that existed for MetaTrader 4 has no MT5 equivalent.
A developer releases an update and an owner installs it over the old file without saving settings. The update resets the risk input to its default, which is higher than the owner had chosen. Three weeks later the owner notices position sizes have doubled. The record for those weeks is at a risk setting the owner never selected, and the drawdown that arrived in week two was the consequence.
None of this is difficult, and all of it goes wrong through haste. Save settings before every change, refuse DLL permissions by default, keep custom indicators from the EA's own developer, and record the date of every update beside the trade history so that the record can be read in versions.