We have a user with "Salesforce Platform" license. How can we give campaigns access to "Standard Platform User" Profile user.
Salesforce platform license does not allow to have access of Campaign object.
Designed for users who need access to custom apps but not to standard CRM functionality. Users with this user license are entitled to use custom apps developed in your organization or installed from Salesforce AppExchange. In addition, they are entitled to use core platform functionality such as accounts, contacts, reports, dashboards, documents, and custom tabs. These users are not entitled to some user permissions and standard apps, including report subscriptions and standard tabs and objects such as forecasts, leads, campaigns, and opportunities.
Access to Campaigns is granted per user, not by profiles, via the Marketing User licence. This license is a kind of Feature Licenses which you can see in the Company Information section for your org. To add a user to this licenese in Salesforce (Classic) go to Setup > Manage Users > Users, then click on the user you want to grant a Marketing User license to.
Unfortunately, Salesforce does not provide access to Marketing License for users with user license "Salesforce Platform".