Downloading the operating system itself (the CAB files, WIN98 folder) without a valid license is software piracy. However, boot disks are utilities. They contain only Microsoft DOS system files, which have been freely distributed for decades for troubleshooting. Most archive sites treat boot disks as abandonware/legacy tools. For safety, always scan any downloaded ISO with VirusTotal, as malicious actors have been known to inject keyloggers into retro tool ISOs.
Once you see A:\> , you are in DOS. Here are the critical commands you'll type: windows 98 boot disk iso