Hi,
One important thing to keep in mind when working within Marketo is that all records are referred to as "Leads", regardless of whether they are a Lead or Contact in SFDC. Each Lead in Marketo
does have a "SFDC Type" attribute on it that will denote whether it is a Lead/Contact in SFDC though.
In regards to your question, I would need some additional background of your two systems. Is your Marketo and SFDC currently synced and passing data back and forth? If so, then you should be able to see leads
and contacts (assuming the profile that is set up for the Marketo sync user has adequate permissions to see these records).
If you are wanting to target contacts specifically, there is a filter called "SFDC Type" under the
Lead Attributes section of the filter sidebar within your Smart List. You can use that filter, and specify:
That will pull all contacts that the Marketo sync user has the ability to see within Salesforce.