Creating a formula for your Expert Advisor (EA) takes time and patience. Here is a breakdown in these basic indicators and help guide for your MQL4 journey.
I have added some of the most popular indicators to have code on. If you are looking to download indicators for your trading please refer to the Indicators tab at the top.
When picking your indicators make sure there is a good flow between them and with the strategy tester, test for multiple years to get how your EA trades in multiple different markets, from flat to bull to bear.