Add-ons are small bits of software that are 'added' to your basic browser to help with doing jobs you want doing.
You say you are using IE 11. Do you have a row of black print very near the top that starts 'File; Edit' and ends with 'Help' ? If you don't, press the 'Alt' key and it will magically appear !
Then click on 'Tools' ( in this line of text ) and you will get a drop-down menu appear which is divided into sections. At the bottom of the second section down, you will see a line which says 'Manage add-ons'. If you click on this, a large box will appear which lists all your add-ons. Now I don't know which add-ons you need, or want, but this is where you will find them. If you are still baffled by what you see here, post back with a list of your add-ons and we will take it from there.
There are known to be some problems with IE 11, I haven't run into any personally but then I don't use very much. It's not my default browser. It does have another feature which may help you, called 'Compatibility view' for web-sites which don't play 'nicely' with IE 11.
Again, click on 'Tools' and you will find it immediately below 'Manage add-ons'. This brings up a small box. At the top of it it says 'Add this web-site'. Type the internet address of the web-site you are having problems with into this box and click on 'Add'. The web-site will then appear in the larger box immediately below the one you typed it into.
As an example, say you bank with the 'Bank of Somewhere' whose web-site is 'Bank Somewhere.com'. Then you just type 'Bank Somewhere.com' into the top box, click 'Add', and it will appear in the larger box.
Hope this helps,