How to do ssh to remote server from Jenkins

For freestyle jobs, you would use the Jenkins SSH plugin.

For pipelines, you have pipeline SSH steps which does the same:

node {
  def remote = [:]
  remote.name = 'test'
  remote.host = 'test.domain.com'
  remote.user = 'root'
  remote.password = 'password'
  remote.allowAnyHosts = true
  stage('Remote SSH') {
    sshCommand remote: remote, command: "ls -lrt"
    sshCommand remote: remote, command: "for i in {1..5}; do echo -n \"Loop \$i \"; date ; sleep 1; done"
  }
}