Put the safety in the off position when aligning the bolt up with the receiver. Preass on the bolt release on the left side of the gun and slide bolt forward. Below is the link to the owners manual for the Browning A-bolt. Recommend downloading it for future reference. Page 6 has the instructions with photos to show how to install bolt.
You can download a manual for free at browning.com
You have a browning a-bolt rifle chambered in .270 winchester caliber.
You need the services of a gunsmith.
In the condition you describe,your browning A-bolt is valued at between 200-350 dollars.
50-500 USD or so
It will be marked on the barrel.
AFAIK they never made a bolt action shotgun
300-400 USd
50-550 usd
500 or so
100-1000 depending on specifics
50-5000 USD depending on specifics.