Indicator cannot be used in an Explorer. You need to create a Exploration for the indicator.
Suppose you wish to explore the Crossover of say 20 EMA goes over 55 EMA and also reversal when 55 EMA goes over 20 EMA
In Metastock Exploration, click New , give it a name and click on ColA and type what is written in your BUY Indicator for the crossover :
Cross(Mov(C,20,E),Mov(C,55,E))
And for the reverse of this , type in ColB
Cross(Mov(C,55,E),Mov(C,20,E))
Why dont you use Metastock formulary guide ! I dont have it but many here can share it with you.