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'.
To add as Custom Html, insert this code anywhere you need:
Full Page Player: <div class="gsp_full_player"></div>