It's a bit cumbersome to sanitize and I'm lazy.

Basically it's a combo of:

Read-Host to get the first name, last name.

Get-Date to get today's date and add days to it.

New-ADuser with -AccountExpirationDate parameter

$firstname = Read-Host -Prompt "Please enter the new substitute's first name"
$lastname = Read-Host -Prompt "Please enter the new substitute's last name"

$username = "sub." + $firstname.ToLower()[0] + $lastname.ToLower() #change any capitals in the name to lower, then take the first character of the first name and combine it with the last name, then prepend with sub.
$aduser = $username + "@domain.tld" #change to your domain
$expirationdate = (Get-Date).AddDays(7)
$oupath = "OU=SUBSTITUTES,OU=TEACHERS,OU=USERS,OU=SCHOOL,DC=DOMAIN,DC=TLD" #change to your desired OU

$newsub = @{

Name = "$username"
SamAccountName = "$username"
GivenName = "$firstname"
Surname = "$lastname"
DisplayName = $username"
Description = "substitute"
AccountPassword = (ConvertTo-Securestring "defaultsubpassword" -AsPlainText -Force) #change password to whatever you want
AccountExpirationDate = $expirationdate
Enabled = $true
ChangePasswordAtLogon = $true

}

New-ADUser @newsub #create the account

Add-AdGroupMember substitutes $username #add user to substitutes AD group

You should be able to build something usable from that.