There are lots of programs for stitching photos to make panoramas.
There are open source (free) programs available. Most are very limited; they often seem to be programming exercises by an enthusiastic developer rather than an attempt to really solve the problem. They will disappoint.
There are programs that charge a wide variety of prices. Before you pay anything, you should try the program. Make sure it runs fast enough on your computer creating the size of panoramas you usually work with.
Adobe Photoshop can stitch photos. It works well, and can do things other programs cannot (e.g. stitch pictures at different focal lengths). The downside of Photoshop: it is very slow, its intermediate files are enormous, and common stitching tasks are inconvenient.
If you have Photoshop and do very little stitching, don’t bother getting dedicated software. If you stitch a lot of panoramas, specialized software is worth the investment.
The leading dedicated stitching programs are Autopano and PTGui. Both come in various versions.
I do almost all my stitching with PTGui Pro.
You need software to lay out any size of image on cut sheets or roll paper. The software must also be able to adjust images based on the printer and paper profile.
Some printers come with their own software. I already had Adobe Lightroom, and it has a super printing feature.