Automatic Data import

Hi,
Using csv is simplest method but you need to create list columns with corresponding csv header name.then try below script, here i create simple script with two column and two csv header so you can change column name and header value in the script and this script based on pnp sharepoint online powershell module so you need to install pnp sharepoint online powershell module . 

$cred= Get-Credential
$Listname= "Listname"
Connect-PnPOnline -Url https://TenantName.sharepoint.com/sites/contosobeta -Credentials $cred
$csv = Import-Csv "C:\Users\csv\users2.csv" 
$ctx=Get-PnPContext
$list= Get-PnPList -Identity $Listname
foreach ($line in $csv)  
{  

$listItemInfo = New-Object Microsoft.SharePoint.Client.ListItemCreationInformation  
    $listItem = $list.AddItem($listItemInfo)  
    $listItem["Listcolumn1"] = $line.Csvheadername1 
    $listItem["Listcolumn2"] = $line.Csvheadername2 
    $listItem.Update()      
    $ctx.load($list)      
    $ctx.executeQuery()  
}

Note:

Before run the script youneed modify following value in the script

$Listname= "Listname"
$listItem["Listcolumn1"] = $line.Csvheadername1 
$listItem["Listcolumn2"] = $line.Csvheadername2