I, no, a

Russian has two words for but, and the distinction between them is the single most useful thing on this page.

но is but in the sense of a genuine objection: the second half contradicts the first. а is but in the sense of a contrast without conflict, closer to the English whereas or an and that sets two things side by side. English collapses both into one word and leaves the listener to work out which was meant. Russian marks it, and getting it wrong is one of the most persistent learner errors there is.

The joiners

и is and. или is or. если is if. когда is when. как is how, and also as or like, and it is one of the highest-frequency words in the language because it does so many jobs.

чтобы introduces purpose, in order that, and it drags a particular verb form along with it. потому appears in the phrase meaning because, and is rarely seen alone.

The particles, which are the hard part

же, бы, ли, ни. These have no dictionary meaning worth learning and are not optional.

же is emphasis and insistence: it tells the listener that you are pressing a point, or that the thing you are naming is the very one already under discussion. бы builds the conditional, and Russian's entire would-have machinery runs through it. ли turns a statement into a yes-or-no question without changing the word order, which is a tidy trick English accomplishes with intonation and an auxiliary verb.

ни is the reinforcing negative, and it is why Russian negation stacks: a sentence can carry several negative elements and they strengthen each other rather than cancelling out.

The rest

тоже is also, даже is even, уже is already. All three are common, all three are straightforward, and they are a welcome rest after the particles.