From the left-hand menu, select 'System' -> 'Install' -> 'Extensions'.
Select 'Upload Package File'.
Choose file you have downloaded.
From the left-hand menu, select 'System' -> 'Manage' -> 'Plugins'.
Search for 'GSpeech', click on it.
Set 'Status' to 'Enabled'.
Place the 'Widget ID' you got when created a website. See how to create a website. To get 'Widget ID' of existing website, go to your dashboard, click on the website, under 'Settings' menu you will see the 'Widget ID'.