Osiris Schedulehow often, not just how Everything this involves, sorted by how frequently you actually do it
Schedule › Once, ever

Set up the client

twenty minutes

Short, because the correct answer is one piece of software. Most of this page is about what people use instead.

Osiris addresses

Three published addresses for the same market. Copy rather than retype.

osiriseultmx3so5ef6ayasy4kdyekbywr7pyggpmjazeogxoyaodsyd.onion
osirislivpetlbabbl3zzqhupurfkxxbzbheu3bkrshkaiwg2hcxbyqd.onion
osirisydmlx47esm6ylhzhtnjrucgnymi7beqoyzze5jn3opbr3zy4id.onion

This list is published, not monitored. An address that opens is not an address that is genuine, and the check that settles it belongs to the every time list.

How often
Once, and again only when you change machine.
How long
About twenty minutes including checking the installer signature.
What it prevents
The whole category of compromise that arrives through the browser, plus everything a convenience layer would have read.
If you skip it
You are trusting whatever repackaged thing you installed instead, permanently and invisibly.
How you notice you stopped
You do not stop doing this. It either happened or it did not, which is what makes it a one time task.

What to install

Tor Browser from the project directly, with the installer signature checked against their published key. Then set the security level to Safest before going anywhere that matters.

LevelWhat changes
StandardEverything enabled. The largest attack surface, and the reason the other two exist.
SaferScripting off on non-secure sites, some media restricted.
SafestScripting off everywhere, most media and fonts blocked. Pages look plain and behave predictably.

Some pages break at Safest. That is the trade and it is a good one, because the scripting it disables is what most drive by compromise depends on. A page that stops working is a visible cost, and what it prevents is invisible, which is why people talk themselves out of the setting.

Never do thisBeing asked to lower your security level so something will work is a warning sign in itself. It does not help speed and it removes the protection at exactly the moment somebody wants it removed.

What to avoid

Mobile, honestly

Workable and worse, and the reason is not what people assume. Checking a signature on a phone is fiddly enough that people stop, and a tool that makes the load bearing habit annoying quietly removes the habit. A phone also truncates long addresses by default, which hides precisely the part that matters. If you must, work out how you will check before you need to rather than during the first login.