The issue you are having isn't actually an issue.
The card space you are referring to is only used by files saved directly to it, photos, music, etc. Not by apps. Your device is looking at the space on it. The "Internal" storage space. A SD card is "External" storage.
Most of the "Internal" storage is taken up long before you get the device by the OS (Android, etc.) and any preinstalled apps. Leaving you only having a small portion of it that you can add things to. This is why you can't add more apps. The only way around that is try try and convert the card to "Internal" storage, if it can be on that device (instructions included below). As for the youtube problems, that wouldn't be the device, that is likely your data/WiFi speed. If you are accessing it via data (through a plan with a carrier/service provider) then you need to check with them. If, however, you are trying to access things online via WiFi, then you need to check that WiFi.
If there are many devices using it, that can cause this. If the speed is fluctuating a lot, that will cause it. Also if the modem/router needs to be reset or if the ISP is having issues this can also cause the problem.
On top of that, if you don't clear out the cache and history of apps you are using, and close apps when not being used (plus restart the device itself regularly) you will run into problems due to the resources on the device not being freed up.
First, you need to be using a tablet that is running at least Android "Marshmallow" (6.0) or newer, or be able to upgrade to it. Second, you will need the instructions I am including below. And third, you need a tablet that has not been restricted by the manufacturer from making this change. Which does happen.
NOTE: If any of the steps are missing on your tablet, or they don't work for you, then you have a tablet that either has an older Android version or has been restricted by the manufacturer. If that is the case, you will not be able to use this information.
How to turn the "External" SD card into "Internal" storage - Option A
NOTE: Please be sure you start with a blank SD card. It needs to be blank because when the card is converted to "Internal" storage, it will be formatted (wiped) and encoded (making the cards data only readable by that device).
1. Go to device “Settings”, then select “Storage”.
2. Select your "SD Card", then tap the “three-dot menu“ (top-right), now select “Settings” from in there.
3. Now select “Format as internal”, and then “Erase & Format”.
4. Your SD Card will now be formatted as internal storage.
5. Reboot your tablet.
so i erased the card and nothing changed ans i unmounted it and it still wanted to erase the card and i is unmounted and the unit says 11gb free and it is a 32gb card so i reboot it and now it still says 11gb of sd card so i take it out and put back in then is sees 31gb. memory info says ram 1gb flash 16gb internal total .98 gb but the batr show 243 available. i clear it and now 492kb used it will not clear lower.
NOTE: If you don't reboot the tablet, many things may not work correctly, so make sure you do.
How to turn the "External" SD card into "Internal" storage - Option B
IMPORTANT NOTE: Be sure you start with a blank SD card. When the card is converted to "Internal" storage, it will be formatted (wiped) and encoded (making the cards data only readable by that device), so anything on it prior would be gone.
1. Go to "Settings", and then select "Storage & USB".
2. At the bottom of the list you should see the SD card's details, including the option to format it and make it "Internal" storage.
3. Once this is done, reboot the device and you can start running things from the card.
NOTE: If you don't reboot the tablet, some things may not work correctly, so make sure you do the reboot.
does not work that info is not there
A Final Note: If you set up the card as "Internal" storage, then the data on it will not be readable by any other device. To access the data you would have to connect the tablet to say a computer and copy it over to the computer from the tablet/card. Otherwise only that tablet can read the data. Also, be sure you do not reset (hard or factory) the tablet. If you do, then all the data on the card will no longer be readable, even by the tablet itself.