Are the pictures on the same device that you are using to access the forum? If so, click the orange, "attach files," button below where you are typing your message
It should then ask you where you want to get the file from.
I'm using my phone mostly these days so these are my options,
I choose files and find the picture or pictures,
And click select.
The pics show up at the bottom of the reply box with options of how to insert them
If posting a few pics with no writing in between you can choose the insert multiple option.
Once you click either thumbnail or full the picture will appear wherever the cursor is
I chose full for everything but these last two,,, not sure if the difference is noticeable.
Doing this from a PC should be similar.
You can also put them on a file hosting site and paste the BBCode where you want them, but I'll let someone else explain that as I find it a pain.