The Exclude Terms by ID lets you skip specific terms. For example, if you wanted to pull in posts by tag but skip a specific tag you could select All Tags from the list and put the tag ID in the exclude terms field. This will skip any posts that have been assigned that tag. The default taxonomy is Category, so if you have "All Terms and Taxonomies" selected then the exclude terms field is for categories.
The Post ID lets you skip specific posts.
The meta key is used in the query to search for specific metakeys (custom field names). It can be used with the sorting options, so if you want to sort your posts into a specific order you can assign them a custom field "order" and assign a number to the field to sort them. Then select to sort (orderby) the posts by numeric metakey.
As for the exclude not working. Are these sticky posts?