To install the Jenkins Artifactory Plugin, go to Manage Jenkins > Manage Plugins, click on the Available tab and search for Artifactory. Select the Artifactory plugin and click Download Now and Install After Restart.

Artifactory Plugin Configuration

To configure your Artifactory server settings, go to the Jenkins System Configuration Page (Manage Jenkins > Configure System).

Click the Add Artifactory Server button to create a new Artifactory server configuration.

Use the Credentials Plugin
Enable this checkbox to use the Jenkins Credentials Plugin to configure your Artifactory Servers credentials in your Jenkins job configuration pages.
Server ID
Configure the Artifactory server (or servers) that will be used for artifacts resolution and build info deployment.
The Artifactory URL.
(Optional) Username and password that will be used for this Artifactory instance. You can also override these credentials from within the Jenkins Job. Note: the credentials are only required if Artifactory is configured not to allow anonymous access.
Use Different Resolver Credentials
(Optional) Enable this checkbox to set different credentials for the resolver.

The Deployer user specified above must have Deploy permission in Artifactory. Log into Artifactory with Administrator privilege, go Security | Permissions in the Admin tab.  Grant Deploy permission to the Deployer user (or perhaps better, a group to which the user belongs).