Select Query condition type (2):

You can use Standard or Advanced config mode to create condition.

Standard Query config mode allows user to create condition using only process data source object fields, while selecting Advanced Query config mode adds Object picklist where user is to choose from the list of available objects (3):

• Click "Add Condition" button
• Fill blank fields with values
• Add more conditions

Values can be of different types: 

• Value - some static value
• Field - values of the the fields of the Source object
• Formula - compare with Merge fields of Context objects using formulas.

Provide condition logic expression if necessary (4):

Condition logic is build based on list of conditions user created.

To use conditions in Logic expression one needs to operate conditions Index (5) values. So {1} will represent Opportunity.Closed = TRUE condition, {2} will represent Opportunity.Fiscal_Quarter = 2 condition, etc.

Following operators can be used when creating logic based on list of indexed conditions:

• OR   evaluates if at least one of multiple values or expressions is true.
• AND   evaluates if two values or expressions are both true.
• NOT(expression that you want evaluated) - Returns FALSE for TRUE and TRUE for FALSE.

( )   specifies that the expressions within the open parenthesis and close parenthesis are evaluated first. All other expressions are evaluated using standard operator precedence.

{BR}  operator is used to create WHERE part of Condition logic. Everything that goes after {BR} works the way clauses do after WHERE statement in Salesforce Object Query Language. Use SOQL SELECT Syntax after {BR} operator.  

• Select Formula condition type.
• Select Context Object and Item and insert to your formula section.

See more on using Context Object at Working with Context objects. See more on using Functions in formula at Using Functions.

• Select Call Apex condition type.
• Select the Class Name in the drop-down. If you don't see your class in the drop-down, use Filter option.
• Enter Parameters in a JSON format.

If run method returns 'true' conditions will not be met and action won't be executed. If action type is 'Rule' error message will be displayed and further actions won't be executed in case action is a part of Global Actions Group.

With the above setup global action will be executed (or will display error message if action type is 'Rule')  if {$Variables.callType} = 'check A' AND {$Variables.A} is not blank or if {$Variables.callType} = 'check B' AND {$Variables.B} = 'BBB'. Otherwise action won't execute.

public with sharing class WR_ApexRulesExpample implements WR_BPM.WorkflowCallApexRuleInterface
{
    public static Boolean run(sObject context, WR_BPM__Flow_Instance_Cursor__c flowInstanceCursor, String parameters)
    {
        Map<String, Object> params = (!String.isBlank(parameters) ? (Map<String, Object>)JSON.deserializeUntyped(parameters) : new Map <String, Object>());
   
        if(params.get('callType') == 'check A') 
        {
            if(String.isBlank((String)params.get('A')))
                return true;
            else 
                return false;
        }
        else if(params.get('callType') == 'check B' && params.get('B') == 'BBB')
            return false;
       
        return true;
    }
}

• Select condition Flow Step Status type

• Process - Name of the Process you want to work with. 
• Version - Version of the Process you want to work with.
• Step - Step you want to work with.
• Status - Select one or several step statuses.

Logic:

•  "All must" - means that selected step should have one of the specified statuses in all active process instances to meet conditions
• "At least one" - means that selected step should be in one of the specified statuses at least in one active process instance to meet conditions 

• Add Conditions to filter records.