Below are the steps to migrate all the posts from one WordPress website to another
Step 1: Log into the old blog that is you source website from where you are about to get exported posts
Step 2: Go to Tools → Export and download the XML (WXR) file from there. During export it will ask to you select content type like post, page, testimonial etc.
Step 3: Login to new blog (the destination website), go to Tools → Import and upload the file you downloaded in step 1. After you upload the file, you can choose the option to Download & import file attachments if you want to move your media files.
With the Import tool of WordPress, You can also have flexibility to take your contents/blogs imported from below sources
*.Categories and Tags
*.Movable Type and TypePad