To create a new post, go to Forums. Tap on the paper and pencil icon top right. Select the Forum board you wish to post in, type a subject line along with your message and tap the white arrows icon top right.
To add a comment to an existing post, open the thread and tap the curved arrow top right. Type your comment and tap the arrows icon top right.
On the website
To create a new post, go to the Forums and select the Forum board you wish to post in and click the green + Add a new post button top right. Type a subject line along with your message and click the green Post button bottom right.
To add a commment to an existing post, open the thread and click the green + Add a comment button top right. Type your comment and click the green Send button at the bottom right.