how to make recent post by category on sidebar widget ?

Hi Fajri,

You'll need a plugin like this one - https://wordpress.org/plugins/contextual-related-posts/ - to display related posts on your sidebar.

changes comma to dot.

Not exactly sure what you mean by this. Can you explain a bit more?

I've using the plugin.
But, the style not same like mastahseo,com :(

Hi there,

that site looks to be using its own custom developed widgets.

If you can share a link to your site we can take a look if its possible to restyle your widgets to match.