ZIP is the file you can send
ZIP remains the archive you can send to anyone. RAR and 7Z are smaller or more familiar in some circles, and creating them needs WinRAR or 7-Zip. What works on this site is the unpack direction: RAR, 7Z, tar, gzip, and bzip2 into ZIP.
Open the ZIP before you delete the original. A password-protected archive will not open here.
If you already know the job, start with 7Z to ZIP or RAR to ZIP.
Every format on the site is listed from the homepage.
Creating RAR or 7Z is a desktop job
Open the tool that names your two formats and read what the download will contain before you delete the original. If a result does not match that description, tell us.
Unpack toward ZIP
ZIP is the archive a phone and a Windows PC can open without an extra install. RAR and 7Z are common for downloads and often smaller, and creating them needs WinRAR or 7-Zip. What works here is the unpack direction: RAR, 7Z, TAR, gzip, and bzip2 into ZIP. The reverse direction that creates RAR or 7Z is not available, and those pages say so.
Gzip and bzip2 sometimes hide a TAR inside. If the ZIP contains one .tar file, you are not finished. Password-protected archives fail. Open the result and read the file list before you delete the original. A ZIP wrapped around a PDF is not a meaningful way to shrink that PDF. Use the PDF tools for a PDF. Very large archives are more reliable on a computer than on a phone. The work runs locally.
After you unpack, open one document inside the ZIP, not only the ZIP itself. A corrupt member can sit beside healthy files. If the download is a single TAR, run the TAR tool next. If the archive asked for a password, stop. There is no password field that bypasses that. Creating 7Z or RAR remains a job for 7-Zip or WinRAR on the desktop. A ZIP that opens on your phone is the file to send to someone else. The smaller RAR can stay on your disk as the download you started with. Do not email a RAR to a person who has never installed an unpacker.
A second look inside the ZIP
After the download finishes, open the ZIP and count the files against what you expected. A photo set of 40 images that arrives as 12 files means the archive was split, password protected, or only partly readable. Do not delete the RAR or 7Z until that count matches. Folder names with odd characters are normal on archives that moved between Windows and Linux. Rename them after you unpack, not before, so you still know which member failed.
Email the ZIP, not the RAR, when the other person is on a phone. If they are a developer on Linux and asked for TAR, use the TAR tool on the ZIP you just made, and tell them the TAR is not compressed. Two steps are honest. One step that produces the wrong kind of file wastes the transfer. Large archives belong on a computer. A phone can run out of memory and leave a partial ZIP that looks complete until you open it.
If you are unpacking on a phone, watch the free storage before you start. A ZIP can be larger than the RAR it came from. When the phone warns that storage is full, stop and move the job to a computer rather than deleting the original archive to make room. The original is the only complete copy until the new one has been opened. Rename the ZIP so it does not match the download name, or the browser may refuse to save the second file.