Store and use password via secure string

write-host "Please enter your password for me to handle with care:"
read-host -assecurestring | convertfrom-securestring | out-file C:\wip\securePassword.txt
$password = (get-content C:\wip\securePassword.txt | convertto-securestring)
$credentials = new-object -typename System.Management.Automation.PSCredential -argumentlist "myusername",$pass

You can then use $credentials in whatever way you wish, e.g.

$remoteSession = New-PSSession -ComputerName $TargetServer -Credential $credentials
Invoke-Command -Session $remoteSession {
	write-host "I'm on the remote computer."

If you want to view that $password as plain text, it's not too easy:

$BSTR = [System.Runtime.InteropServices.Marshal]::SecureStringToBSTR($password)
$plainText =  [System.Runtime.InteropServices.Marshal]::PtrToStringAuto($BSTR)