Marketing Clouds and Sales Cloud are connected. There are some leads in Sales Cloud. I am creating a journey in MC and want to use 'data extension' from sales cloud. How is it feasible? Is there a way to convert sales cloud leads into data extension and then use it in MC journey?
For triggering a Journey, based on data from Sales Cloud, I will recommend using Salesforce Data Event. This will inject the lead into the journey in near real time. You can set criteria for which leads should be injected, and whether these criteria should be evaluated only on record creation or also on update.
When creating Salesforce Data Event, you can also select which fields from the injected record or related records you want to include for the journey to use. These fields will be stored in Journey Data, and can be used for personalisation in emails, and for decision splits throughout the journey. Please do keep in mind, that Journey Data are static, and represent the snapshot of how data looked at the time when the lead was injected. You want to use Contact Data for referencing the current state of your contact. This document summarises key differences between Contact and Journey Data.
When you want to use some of the data from Sales Cloud as Contact Data, you need to connect Sales Cloud objects ans Synchronised Data Sources. This will create a number os Synchronised Data Extensions that represent your objects in Sales Cloud. Once configured, please verify these Data Extensions are connected in Data Designer, and the relationships are correct. When this is done, you will be able to use them in Journey Builder.