If you want to have your question answered quickly and avoid many back and forth, you should read this excellent article with lots of useful tips. One of them is providing sample data. To describe your problem, it is often very helpful if you make a screenshot of your table(s) and paint or annotate the logic you want to achieve. A picture is the perfect medium for it and everyone is allowed to upload those. However, in addition to that, sometimes the problem can best be solved by playing with the data or some sample data (if the original data is confidential or too large). There are some things to consider for doing so:
1) Uploading files
Especially when you have a problem with a DAX statement or the data model, it would be best to provide a pbix-file containing the sample data. You might have seen posts here in the forum where files are directly attached and have searched for the button to do exatly that. But unless you're a Microsoft employee or a super user this feature will not be available for you. Instead you have to upload your file to a cloud storage (like OneDrive, Dropbox, Google Drive or Wetransfer for example) and paste the link to that storage location in the post.
2) Pasting tables into the post
Another way is to paste table(s) with the sample data directly into the post. If you do that, it's important that this results in proper HTML-tables because otherwise it will become difficult to copy that data into the tools to work upon. The following steps show how easy it is:
2a) Only take data that you've copied from a spreadsheet
Please don't copy the data directly from Power BI to the post. This will most likely mess up the headers and other elements as well.
Also, if your data comes from another webpage or wherever: Copy it first into a spreadsheet.
Select the data in the spreadsheet and copy it there.
2b) Use the "Table"-button to insert your data.
If you don't see that button, that means that the current web page is not fully rendered yet. Wait a bit for it to appear.
2c) Select just ONE field in the table
Table --> Table -> select just ONE (!) field (irrespective of the size of the copied data)
2d) Paste the copied table content
Place your mouse into the box:
paste with Ctrl + V (or Strg + V)
2e) Check the results
The header row should be identifiable as such:
But if your data looks like so, something went wrong:
This is probably due to some messed up HTML formatting. I would start a new thread to paste this data instead. Close the current thread and give a hint that further content is coming. Pasting into a fresh thread should be the quickest way going forward.
Please have in mind that you cannot post very large tables directly into the post, as the size is limited to 20.000 characters per post. (Counting the characters in the HTML-code).
Anything I've missed? Please let me know in the comments below.