Discourse creating posts
Click the "New Topic" button on the home page or a Category screen. Make sure that you are posting to the desired category. You can use the rich text editor to format your post including adding images, links etc. You can refer to other users using the at symbol eg @Chris_Cant. Click on "show preview" (bottom right) if you want to see what the post will look like.
Note: when starting a reply, if you click on the top left editor icon, you can opt to "Reply as a linked topic" ie start a new linked topic.
You can edit your own topics and replies. You can delete your replies (it says "post withdrawn" for 24 hours before disappearing; this time can be configured). To delete a topic, flag it for the attention of moderators.
Moderators can pin topics to the top of a category.
Polls
You can include a poll in a new topic. When the topic editor appears, click on the ⛭ settings cog within the editor window and choose "Build poll". There are various options: single choice, multiple choice and number rating and you can choose if you want to show the results during the poll. You can opt to close the poll at a specified time - or close it manually when you want.
Don't forget to add a good title for your post and some explanatory text if need be. Check your wording carefully as you can only edit a poll for 5 minutes after creation.
Scheduled posts
Admins and moderators can do scheduled posts: https://meta.discourse.org/t/how-to-create-a-timed-topic/60731 However regularly repeating emails aren't possible.