After you click on the browse button, you need to find where the picture file is located in your computer.
Is it in "My documents", "My Pictures" etc?
You need to click on the checkmark to open up the box with all of your computer files to browse through.
Then to the far right of the checkmark, there is a little blue and white box where you can click on another checkmark to open a list where you want to click on "Thumbnails" to help you see the actual photos to choose from in the larger browse box.
Then after sifting through files and thumbnails, click on the picture to select it by simply clicking on it, and then the "open" tab. Then it will be ready to upload and all you need to do is to just click on the "upload" tab and it will become a thumbnail to your post. If it's not within size limits then a message will tell you that.
I suggest to close the "manage attachments" window after the upload are completed but before you save the post because sometimes the uploads are lost. You can always reopen the manage attachments window and upload more pictures or to edit/delete them.
After the period of time when being able to edit your post has passed, the pictures can be found/deleted by clicking on "User CP" found at the top left row of every page, and then "attachments", and then "show thumbnails".
There's a box to check for each uploaded picture, and then click on "Delete selected".
I suggest to upload any picture to just give it a try to see if you can do it, and then delete it so you can practice selecting photo files stored within your computer.
Where in your computer or in which folder do you store your picture files?
You need to find the location/heading and/or title where they are located.