To connect your LinkedIn Profile and Pages to Postcron click on the + sign button at the top right side of the screen, and then choose LinkedIn.
If you're already logged into your LinkedIn Profile, you'll be shown that Profile and a list of the Pages it manages in different tabs. If you aren't, you will be prompted to log in. Make sure you log into the profile that has an admin role to the page you're looking into connecting.
Then, you just have to click on the + button next to each Page or Profile to connect them to Postcron.
Postcron will request that you accept publishing permissions in order to post to your social accounts on your behalf. Make sure you accept all of them to avoid future publishing problems.