Your post isn't that clear but it sounds like the game is crashing because that is the only time the launcher will tell you that you are using an unsupported modified version (example). In that case, click on the "view crash report" link and paste it into a spoiler, or to a site like Pastebin and post the link (if there is no crash report copy the game output; it it doesn't appear go into launcher settings and check that "open output log when game starts" is enabled).
Otherwise, if the game itself is telling you something about an issue with mods (example) then you may be using incorrect or incompatible mods; a screenshot and/or log will help to pinpoint the issue.
i keep adding mods and when i load it up it says im using unsupported mods. What does this mean?
Mojang allows the use of modifications to its game, but does not support modded MC. That is a standard statement from the company.
"We live on a placid island of ignorance in the midst of black seas of infinity, and it was not meant that we should voyage far."
Your post isn't that clear but it sounds like the game is crashing because that is the only time the launcher will tell you that you are using an unsupported modified version (example). In that case, click on the "view crash report" link and paste it into a spoiler, or to a site like Pastebin and post the link (if there is no crash report copy the game output; it it doesn't appear go into launcher settings and check that "open output log when game starts" is enabled).
Otherwise, if the game itself is telling you something about an issue with mods (example) then you may be using incorrect or incompatible mods; a screenshot and/or log will help to pinpoint the issue.
TheMasterCaver's First World - possibly the most caved-out world in Minecraft history - includes world download.
TheMasterCaver's World - my own version of Minecraft largely based on my views of how the game should have evolved since 1.6.4.
Why do I still play in 1.6.4?