Using campaigns within zoho CRM

Using campaigns within zoho CRM

Can someone assist with how i should use a campaign within Zoho CRM. I have created 3 campaigns but it doesn't appear to flow how it want it to. I think i'm using it back to front. I've created a campaign using existing leads, e.g. i have leads that are 90+ days old and i have imported these into a 'Campaign' so that they can be refreshed however i am finding it difficult to work these within the dedicated campaign. 

After reading the help menu i think that you start an activity (external to Zoho CRM) from a trade show, then when you get interest at the show you add this person as a lead, this doesn't work for me. Can someone help with how i would use Zoho CRM or one of its components to 'work' my leads 90+days old to re-target my older leads?