To display email subscription box you will need to sign up for feedburner or similar service provider. Then the feedburner will provide you email subscription form code on their website. It will be under Publicize tab. Copy and paste this code in a TEXT widget on your website.
To display an RSS link button in a text widget here is what I do:
I find an RSS image icon suitable to my site’s design and placement.
Then I upload that image to my wordpress installation. In the left sidebar under your blogs admin section you will see a link “Media” go there and upload your rss image icon.
Once the image is uploaded it will you the path to that image file on your webserver.
now add this code to a text widget in your sidebar: Replace yoursite.com with your blogs adddress and image path with the location of RSS icon on you uploaded.
<a href="https://yoursite.com/feed/" title="Subscribe"><image src="image path" alt="subscribe" /></a>