Minecraft mods don't go through twitch?

When I tried to install mods for Minecraft with the Twitch Launcher, it worked, but who; I then pressed play on the Minecraft launcher, there was an error message and that something went wrong. How else can I install mods or how can I fix it with the twitch launcher

(have Windows7)

Some mods are not compatible with each other because block / itemIDs may overlap. Some mods also need a certain core mod (version). The Coremods are usually installed directly in Twitch. So I suspect there's another mistake. The best thing to do is check out the logs. These should be able to help you there.