Here's Samson Ropes web site for splicing:
There are a number of web sites that can help you. Do a Google search.
You must know your rope, though. Not all halyards are double braid. Some have a laid core, and the splicing technique is quite different.
Splicing is important. Knots are far weaker than splices. You need to do it correctly, or you may as well not do it at all. You also need to have the correct gear. Splicing fids are important.