Understanding the code

Function Get-SystemInfo { #Create Function
    param( #Create Paramater
        [string[]]$ComputerName = 'localhost'#Create an Array of Strings ALL named $ComputerName: ie $ComputerName = @("ComputerName","ComputerName")
    )


    begin{ #Start giant script block, I'm confused by begin an end, why is this needed? If it is all in the function, isn't that enough?
        $comps = @() #Create new empty array to be used at a later time
    }

    process{ #This represents another script block?
    ForEach ($computer in $ComputerName){  #ForEach loop For every $computer which we JUST created in this ForEach loop: $ComputerName run the switch below.

        $AdminPasswordStatus = Get-CimInstance -ClassName Win32_ComputerSystem -ComputerName $computer | Select-Object -ExpandProperty AdminPasswordStatus #Create variable = to this value
        switch ($AdminPasswordStatus) #Switch, this one is pretty simple.
            {
                1 {$AdminPasswordStatus = "Disabled"}
                2 {$AdminPasswordStatus = "Enabled"}
                3 {$AdminPasswordStatus = "Not Available"}
                4 {$AdminPasswordStatus = "Unknown"}
                default {"Possible Error"}
            }

        $OS   = Get-CimInstance -ClassName Win32_OperatingSystem -ComputerName $computer #Create variable = to this value
        $BIOS = Get-CimInstance -ClassName Win32_BIOS -ComputerName $computer #Create variable = to this value

        #Everything below this point is new to me but I'm going to try to follow the logic.

        $obj = [pscustomObject]@{ #Create a custom object, This is neat I did not know this.
            ComputerName = $computer
            AdminPasswordStatus = $AdminPasswordStatus
            OSVersion = $OS.Version #Get-CimInstance -Classname Win32_Operatingsystem.property which is Version
            OSPatch   = $OS.ServicePackMajorVersion #Get-CimInstance -Classname Win32_Operatingsystem.property which is ServicePackMajorVersion
            Bios      = $BIOS.SerialNumber #Get-CimInstance -Classname Win32_BIOS.property which is SerialNumber
            }

        #end of the ForEach loop, we now store this $obj in $comps
        $comps += $obj #This one is confusing. This means I have more than one $comps so you will need to make an $obj for each $comps?
        }
    }

    end{#End giant script block, I'm confused by begin an end, why is this needed? If it is all in the function, isn't that enough?
    Write-host ("`$comps contains " + ($comps.Count) + " Objects") #Output how many computers you are running this script on.
    $comps | Format-Table #Change output to Format-Table
    }
}


Get-SystemInfo #Call Function