To get a good quality experience in Craft or in OpenSim in general, you need a good internet connection and a pc that meets the minimum features described below.

Connection:
Generally a DSL connection with at least 4 Mbit/s in download and 1 Mbit/s in upload may be enough. If the connection is shared with other people (in your family or in your office) then it would be better to consider connections with higher bandwidth.
However, some satellite or wireless connections are not compatible with OpenSim.

PC:
Operating system: Windows (8.1 to 11, 64-bit), MacOS (preferably the latest official version), Linux (a modern 32-bit version or a 64-bit version with 32-bit compatibility environment).
RAM: 4GB or more.
Video Card: A suitable video card to support 3d games is required. *
CPU: A modern Intel or AMD processor of at least 2GHz is generally more than enough.

If you meet the required characteristics, register your avatar here:
https://www.craft-world.org/page/en/register-an-avatar.php

Now you will have to download an easy-to-install program, the viewer for OpenSim, through which you will be able to access the 3D contents.

Among the different viewers available, we recommend the most popular to start with, Firestorm, which you can find here:
https://www.firestormviewer.org/choose-your-platform/
Select Download Firestorm Viewer for Open Simulator then click on the icon that represents your operating system (Windows, MacOS or Linux).

Install and open the viewer, select Craft World from the grid list, enter the avatar name and password and welcome to Craft!
And now?

WORK IN PROGRESS - There will be more soon.

*) At least an Nvidia GeForce 10 series (1030, 1050, 1060 etc.) or better or AMD Radeon RX 500 series (550, 570, 580 etc.) or better is required for an acceptable experience. If you are planning to buy a new PC with good features for OpenSim, buy one with a video card higher than those listed above which are the minimum for those who already own them.