Am getting an error while trying create a project using swarm environment

This is the error am gettings. quick question whats the difference if I create project or I just create stack in the system section

Error (exit status 1: Creating staging_frontend_1 Creating staging_redis_1 Creating staging_db_1 Creating staging_rabbitmq_1 Creating staging_web_1 Unable to find a node that satisfies the following conditions [available container slots] [–link=staging_db_1:db --link=staging_db_1:db_1 --link=staging_db_1:staging_db_1 --link=staging_rabbitmq_1:rabbitmq --link=staging_rabbitmq_1:rabbitmq_1 --link=staging_rabbitmq_1:staging_rabbitmq_1] )