Obviously masturbation is a very serious sin. However, if someone has already transgressed that sin, does his status change vis-a-vis things like learning Torah or davening? Does he need to go to a mikvah before engaging with things that are related to kedusha?
Masturbation per se does not change one's halachik status at all, although it does generate an obligation to repent.
Ezra originally established that a man who is impure from any seminal emmision (not just masturbatory) cannot say shema, pray or say other blessings until he has gone to the mikva. However this decree was later rescinded, and the law and the popular custom is not to change one's liturgical practices if one is impure. (Shulchan Aruch OC 88)
In general, one's status does not change, and one should not feel that one is prohibited from learning or davening. That said, it is important to take steps to rectify this very serious sin.
Aside from the necessary steps for teshuva regardless of the sin, one should go to the mikvah as soon as possible - if one is not available, a shower will do - and recite the Tikkun HaKlali. It is preferable to do so in Hebrew but English works if one cannot read Hebrew. These ten psalms were set out by Rebbe Nachman of Breslev zy'a as a means by which to completely repair emissions outside of normal marital relations.
Beyond this, the Baal HaTanya recommends fasting, but in our day the amount of fasting required is not possible, so it suffices to give substantial amounts to charity.
Above all else, the main way to fight this is to get married as soon as possible!
Let me add a couple things, based on English-language responsa on the Institute for Dayanim website.
"Cleaning off Zera" says the principal halacha is that you can pray even with semen on your clothing. It adds that if you masturbated, it's "proper" to wash your bedsheets to remove semen. The responsum uses the term "proper", not the term "obligatory". Read it yourself and decide if washing them is really required or not.
"Contaminated Clothing" adds that washing items in the normal way is sufficient to deal with all halachic concerns.
The website doesn't specify who wrote each responsum. The site's responsa section's chief halachic editor is R' Yehoshua Pfeffer.
He is disqualified to serve as a witness in a beit din, or at a wedding. This is not unique to someone who masturbates, rather any person who has violated a torah law or a rabbinic law, and who has not repented, is disqualified.