There are some themes that ask you to upload images to a Post but not to insert them or to create a gallery. This can be counter-intuitive so here are some step by step instructions for doing this.
Create a new Post or Page or navigate to the Post or Page you wish to edit. Then click on the “Add Media” button.
This will open a new window: Insert Media. To add an image you have not previously used, click Upload Files. You can either drag an image into the drop area, or click Select Files, and chose an image from your computer. You can add multiple images at a one time.
(Note: To attach images to a Post you cannot choose an image uploaded to another Post. Images must be uploaded to the particular Post.)
Once you’ve chosen your image, it should appear as a thumbnail, with a blue box around it. You can now enter any details that you would like to accompany the image. Under Attachment Details along the right side, fill in the image’s details, such as title, caption, and description. This information will appear with the image depending on how your theme is designed. Be sure to read your theme instructions carefully.
Close the image uploader by clicking the “X” in the upper right hand corner. (This is the counter-intuitive part). Do not click “Insert into Post”. The images because they have been uploaded to this Post are now attached to the Post and the images will be displayed according to your theme’s design.
Be sure to click “Update” or “Publish” to save changes. Check the Post or Page to view the changed order.