Tires on bike won't move and derailleur issue

[Nlghtt]

For starters im new to biking and have started trying to do it for the exercise so excuse my poor knowldege on bikes. I have had my huffy mountain bike for years stored in the garage never touched once until today. I filled the tires with air and then when i proceeded to try to ride the bike the chains would clank. The video shows all the problems im having visual and whatnot. It's especially prominent when im backpedaling.

https://www.youtube.com/watch?v=Ua2ilU_nu7A

[ReapThaWhirlwind]

The video is removed it says, but maybe;

Try to reindex the rear derailleur from scratch. Shift down into the smallest cog, and unlink the cable from the derailleur. Dial the barrel adjuster in all the way (like tightening a bolt—turning it clockwise). Slightly tug the cable to gently remove slack and refasten it down with the anchor bolt. Slowly, in small increments, begin to dial the barrel adjuster out (counter-clockwise) and try to shift up. If it doesn't shift up, shift it back down and dial the barrel adjuster out a little more. Keep doing this until shifting ascends and descends smoothly. Dial the barrel adjuster back in if you have trouble downshifting.

Also check the high limited screw (HL marked screw) on the rear derailleur. When shifted all the way down into the smallest cog, dial this screw all the way out, then peek inside so you can see the screw and the anchor piece it contacts with. Dial the screw in until it just subtly pushes the metal anchor point in to brace it.

[meamoantonio]

Coudnt view the video either but from what you described I think the chain's lube has dried up and has now lost its ability to move with the crank and cogs, you can add bike chain lube and let it seep in for a few hours then try again

[Talha]

Based on what I read (not viewed lol).

it sounds like there could be a few potential problems causing the clanking sound and issues with the chain. So, let's start thre.
The clanking sound and difficulty backpedaling could be due to improper chain tension. If the chain is too loose, it may slip or make noise. Conversely, if it's too tight, it can cause excessive friction and noise. So (1) check the chain tension

2) Lubricate

3) Check for any damage beyond repair to the chain or crankset.

4)The clanking sound could also be related to the cassette or freewheel on the rear wheel. These components have individual cogs that can become loose or damaged over time. If you suspect an issue with the cassette or freewheel, it's best to have it inspected by a bike mechanic