In short there will be a number of installs and configurations you will have to perform, follow this for Splunk Strem components.
https://docs.splunk.com/Documentation/StreamApp/8.1.1/DeployStreamApp/AboutSplunkStream
High Level Steps
1.Design your architect and the data flow - ensure all ports required can communicate
2. Ensure your device can send netflow data
3. Configure a Splunk index for the netflow data in Splunk
4. Configure Splunk HEC in Splunk and set it to the netflow index
5. Install and Configure the Splunk netflow componenets (ISF) this is where you would point the device to send its netflow data, which then sends to Splunk HEC.
Follow this for Splunk HEC configuration
https://docs.splunk.com/Documentation/SplunkCloud/latest/Data/UsetheHTTPEventCollector
Flow this for your architecture - there is a good diagram that you need to consider for all the componenets
https://docs.splunk.com/Documentation/StreamApp/8.1.1/DeployStreamApp/DeploymentArchitecture
Example of stream in action
https://lantern.splunk.com/Data_Descriptors/DNS_data/Installing_and_configuring_Splunk_Stream
