If you wish to hide/show sections of your document based on certain conditions then you can surround that text with conditional merge fields (IF, ELSEIF, ELSE)

Syntax

...

[[*IF {FirstName|pt=Client|rn=*} == "James" *]] Hello Jim [[*ENDIF*]] 

The * denotes that we're doing something special while the IF starts the conditional statement

[[*IF

The standard merge fields from your merge field list should be included in braces (otherwise known as "curly brackets")

{FirstName|pt=Client|rn=*}

Any static values should be included in quotes and there should be an operator in front of that static value

="Steve"]]

The text that you wish to display should follow the conditional start field 
Hello Steve 

Finally, you will need to include a conditional field stop

 [[*ENDIF*]] 

You can add any number of ELSEIF options for additional conditions and ELSE section as a catch-all if all prior IF/ELSEIF conditional are false

Example

The Client's Nickname is: [[*IF {FirstName|pt=Client} == "James" *]] Jim [[*ELSEIF {FirstName|pt=Client} == "Robert" *]] Bob [[*ELSE*]] [[FirstName|pt=Client]] [[*ENDIF*]]

Conditions Dependent on Record Number

...

Say I was already displaying the Full Name of all the Clients entered into my matter with the following Repeat Block:

[[*REPEAT|source=action_participant.Client|tablerow|*]] [[FullName|pt=Client|rn=*]] [[*REPEAT|END*]]

So that it generated the following result:

Sam Jones

Danielle Smith

Christine Yang

...

Now say I wanted the text 'BETWEEN' to appear before the first Client's name, and the text 'AND' to appear before every other client's name, so that is generated in my table like:

BETWEEN  Sam Jones

AND            Danielle Smith

AND            Christine Yang

To produce this I could enter a conditional merge field into my repeat block depending on the record number being generated. The code I would add would be:

[[*IF {FullName|pt=Client|rn=*} == {FullName|pt=Client|rn=1} *]] BETWEEN [[*ELSE*]] AND [[*ENDIF*]]

So my full merge field including the repeat block would be: